MuItiwavelength
AGN Surveys
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Proceedings of the Guillermo
Haro Conference 200
Multiwavelength
AGN Surveys Cozumel, Mexico
8 - 12 December 2003
editors
Raul Mujica lnstituto Nacional de Astrofisica, dptica y Electronica, Mexico
Roberto Maiolino INAF-Osservatorio Astrofisico di Arcetri, Italy
K$World Scientific N E W JERSEY * LONDON * SINGAPORE
B E l J l N G * S H A N G H A I * HONG KONG * TAIPEI * C H E N N A I
Published by World Scientific Publishing Co. Pte. Ltd. 5 Toh Tuck Link, Singapore 596224 USA ofice: 27 Warren Street, Suite 401-402, Hackensack, NJ 07601
UK ofice: 57 Shelton Street, Covent Garden, London WC2H 9HE
British Library Cataloguing-in-PublicationData A catalogue record for this book is available from the British Library.
Cover: Copyright Bonampak Documentation Project Reconstruction painting by Heather Hurst
MULTIWAVELENGTH AGN SURVEYS Proceedings of the Guillermo Haro Conference 2003 Copyright 0 2004 by World Scientific Publishing Co. Pte. Ltd. All rights reserved. This book, or parts there05 may not be reproduced in any form or by any means, electronic or mechanical, includingphotocopying, recording or any informarion storage and retrieval system now known or to be invented, without written permission from the Publisher.
For photocopying of material in this volume, please pay a copying fee through the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, USA. In this case permission to photocopy is not required from the publisher.
ISBN 981-256-049-1
Printed in Singapore by World Scientific Printers ( S ) Pte Ltd
Scientific Organizing Committee Chris Carilli, Deborah Dultzin, Alberto Franceschini, Reinhard Genzel, Jose Guichard, Giinther Hasinger, Luis Ho, Roberto Maiolino (Chair), Michael Straws, Philippe Veron, Belinda Wilkes
Local Organizing Committee Raul Mujica (Chair), Erika Benitez, Miguel Chavez, Vahram Chavushyan, Divakara Mayya, Jose Ramon Valdes
Supported by Instituto Nacional de Astrofisica, Optica y Electr6nica (INAOE) Consejo Nacional de Ciencia y Tecnologia (CONACyT)
V
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Contents Preface
xvii
Part I. AGN Surveys X-ray Surveys A Long, Hard Look a t the X-ray Background - The Chandra Deep Fields ........................................................... F. Bauer
5
High Energy Large Area Surveys and the History of Accretion in the Universe ............................................................. F. Fiore
11
X-ray spectra of XMM-Newton AGN from Medium and Deep Surveys 17 S. Mateos, X . Barcons, F.J. Carrera and M. T. Ceballos Unveiling the AGN Population with ChaMP’s X-ray Vision .......... 21 J . Silverman, P. Green, B. Wilkes, W. Barkhouse, D. Kim and T. Aldcroft The XMM-Newton12dF Survey ...................................... A. Akylas, I. Georgantopoulos, A. Georgakakis, 0. Giannakis, S. Kitsionas, M. Plionis, S. Basilakos, V. Kolokotronis, G. C. Stewart, T. Shanks and M. Vallbe Galaxies a t the Limit of Deep X-ray Surveys: Galaxies or AGN? R. E. Grifiths, A. Knudson and T. Miyaji
. . . . . 29
X-ray Spectral Fitting of AGN in the ChaMP ........................ T. L. Aldcroft, J . D. Silverman, P. J. Green, D.-W. Kim, W. A. Barkhouse, R. A . Cameron, A. Mossman, B. J. Wilkes, H. Ghosh and B. Jannuzi vii
25
33
viii
X-ray Colours of AGN in the 13h XMM/Chandra Deep Field ........ 35 T. Dwelly and M. J. Page The Serendipitous Extragalactic X-ray Source Identification (SEXSI) Program ............................................................. M. E. Eckart, F. A . Harrison, P. H. Mao, S. A . Yost, D. J. Helfand, E. S. Laird and D. Stern
37
Preliminary Results from the XMM Medium Deep Survey . . . . . . . . . . . . 39 L. Maraschi, M. Tajer, G. Trinchieri, L. Chiappetti, L. Paioro, D. Maccagni, M. Pierre, J. Surdej and 0. Le Fbvre Exploring the Hard X-ray sky with XMM-Newton .................... 41 E. Piconcelli, M. Cappi, L. Bassani, G. Di Cocco and M. Dadina X-ray Number Counts of Star Forming Galaxies ...................... P. Ranalli, A . Comastri and G. Setti
43
Optical and Infrared Surveys The SDSS Quasar Survey(s): Probing the Physics of Quasars ......... 47 G. Richards, P. B. Hall, M. A . Straws, D. E. Vanden Berk, D. P. Schneider and T. A . Reichard The Distribution of Quasars and Galaxies in Radio Color-Color and Morphology Diagrams ................................................ 53 Z. IveziC, R. J . Siverd, W. Steinhardt, A . S. Jagoda, G. R. Knapp, R. H. Lupton, D. Schlegel, P. B. Hall, G. T. Richards, J. E. Gunn, M. A . Straws, M. JuriC, P. Wiita, M. GaCeSa and V. SmolEiC The 2dF QSO Redshift Survey ....................................... S. Croom, B. Boyle, T. Shanks, P. Outram, A . Myers, R. Smith, L. Miller, A . Lopes, N . Loaring and F. Hoyle
57
Evolution of Optically Faint AGN from the COMBO-17 and GEMS . . 63 L. Wisotzki, K. Jahnke, S. F. Sanchez, C. Wo& M. Barden, E. F. Bell, A . Borch, B. Haussler, K. Meisenheimer, H.- W. Rix, S. V. W. Beckwith, J . A . R. Caldwell, S. Jogee, R. S. Somerville, D. H. McIntosh and C. Y . Peng X-ray and Optical Number Counts of AGN in the GOODS Fields . . . . 69 M. Urry and E. Treister
ix
Measuring the Luminosity Dependence of Quasar Clustering using the 2dF QSO Redshift Survey ........................................ N . Loaring and L. Miller
73
IR Spectroscopy of the Most Distant QSOs. .......................... R. Mujica, R. Maiolino, Y. Juarez, E. Oliva, N . Nagar, F. Ghinassi, M. Pedani and F. Mannucci
77
Are QS02 Hiding Among EROs? .................................... M. Brusa
81
The Nature of the Sources of the Mid-IR Background Light .......... 85 C. Shchez-Ferna'ndez Hot Dust in Radio-loud AGNs ....................................... W. Freudling
89
A Deep Wide-field Infrared Survey for Quasars ....................... 93 R. F. Green, S. Croom, S. Warren, P. B. Hall, M. Brown, A . Dey, B . Jannuzi, M . G . Smith, D. Norman, G. Tiede and P. S. Smith 3C 345: The Historical Light Curve (1966-1991) from the Digitized Plates of the Asiago Observatory ..................................... A . Omizzolo, C. Barbieri and C. Rossi The Peculiar Variability of PKS 0736+017 ........................... A . Ramirez, J.A. de Diego, D. Dultzin-Hacyan and J. N. Gonzdez-Pirez
95 97
Predictions for the Infrared Observations of GOODS AGN . . . . . . ..... 99 E. Treister and C. M. urn^ The P a o Deficit in IRAS 20100-4156 ............................. J. R. Valdes, A . Bressan, S. Berta, A . Franceschini, G. Rodighiero and D. Rigopoulou
101
Molecular Emission in LIRGs and ULIRGs ....................... 0. Vega, A . Bressan, G. L. Granato, M. Chavez, L. Carrasco, D. Mayya and L. Silva
103
The Nature of the Optical Emission in Ftadio-Selected AGN ...... M. T. Whiting, R. L. Webster, P. Majewski, A . Oshlack and P. J. Francis
105
X
Radio and Millimeter Surveys Redshifted Far-infrared/submm Dust Emission from High-z QSOs . . . 109 A. Omont, A . Beelen, F. Bertoldi, C. L. C a d i and P. Cox Molecular Gas in High Redshift QSOs .............................. C. Caralla, F. Bertoldi, F. Walter, K.M. Menten, A . Beelen, P. Cox and A . Omont
115
The GTM/LMT Project Status ..................................... L. Carrasco, E. Recillas and F.P. Schloerb
123
What Powers High-redshift SCUBA Galaxies? ...................... D. Alexander
129
A Large Area Search for Radio-loud Quasars within the Epoch of Reionization ........................................................ M. J . Jarvis, S. Rawlings, F.E. Barrio, G.J. Hill, A . Bauer and S. Croft
133
Testing the Homogeneity of Bright Radio Sources at 15 GHz . . . . . . . . 137 T. G. Arshakian, E. Ros, J . A. Zensus and M . L. Laster Understanding the Relationship Between the Environment of the Black Hole and the Radio Jet: Optical Spectroscopy of Compact AGN ................................................... T. G. Arshakian, E. Ros, J. A . Zensus and V. H. Chavushyan
139
The 6C** Sample and the Highest Redshift Radio Galaxies . . . . . . . . . 141 M. J. Cruz, M. J. Jarvis, K. M. Blundell and S. Rawlings The FIRST Flat Spectrum Sample .................................. G. Fossati
143
The Cosmological Evolution of the Environments of Powerful Radio Galaxies ............................................................ J. A . Goodlet and C. R. Kaiser
145
Consistency Between the Radio & MIR Source Counts using the Radio-MIR Correlation ............................................. N . Seymour, I. McHardy and K.F. Gunn
147
xi
Part 11. Results from Surveys Statistical Properties of Local AGN What Can We Learn from Nearby AGNs? .......................... L. C. Ho
153
AGNs in the Mid-Infrared .......................................... E. Sturm
163
Radio Properties of Local AGN ..................................... N . M. Nagar, H. Falcke and A . S. Wilson
169
A Far-ultraviolet Spectroscopic Survey of Low-redshift AGN . . . . . . . . 179 G. Kriss A Survey of Extended [OIII] Emission in Seyfert Galaxies . . . . . . . . . . . 183 H. Schmitt Nearby Case Studies: The Building Blocks for Interpreting Surveys N. A . Levenson, T. M. Heckman and K. A . Weaver Using the X-ray Emission Lines of Seyfert 2 AGN to Measure Abundance Ratios .................................................. M. A . Jimenez-Garate and T. Khu
.
187
191
Extinction Curve Toward the Nuclear Region of M82 ................ 193 L. Hernandez-Martinez and D. Mayya The AGN Pair NGC 5953/54: BVRIHaJK Photometry and [NII] Fabry-Perot Interferometry ......................................... H. M. Herna'ndez- Toledo, I. Cruz-Gonza'lez, I. Fuentes-Carrera, M. Rosado, A . Franco-Balderas and D. Dultzin-Hacyan
195
Statistical Properties of High-ionization Forbidden Emission Lines of 197 Seyfert Galaxies .................................................... T. Nagao, T. Murayama and Y. Taniguchi Profile Variability of the Ha: and HP Broad Emission Lines in NGC 5548 .......................................................... A . I. Shapovalova et al.
199
BVRI Surface Photometry of the Seyfert Galaxy SBS 0748+499 . . . . . 201 J . Torrealba, E. Benitez and A . Franco-Balderas
xii
Unification and Unconventional AGN Unification of Radio-quiet AGNs: Successes and Failures ............ 205 S. Veilleux New Insights on Unification of Radio-loud AGN ..................... M.Chiaberge GBT Monitoring and Surveys for HzO Maser Emission in AGNs J. Braatz, C. Henkel, L. J. Greenhill, J. M. Moran and A. S. Wilson
217
. . . . 227
Obscured AGN and Type I1 QSOs in Chandra Cluster Fields . . . . . . . 231 P. Gandhi, M. Worsley, C. S. Crawford and A . C. Fabian Elusive AGN ....................................................... R. Maiolino and L. Zappacosta
235
Transmission- to Reflection-dominated Transition in Seyfert 2 Galaxies: the XMM-Newton View ................................. 239 M. Guainazzi, P. Rodriguez-Pascual, A. C. Fabian, K. Iwasawa, G. Matt and F. Fiore Physical Processes Behind the Alignment Effect S. Mendoza and J. C. Hidalgo
.....................
243
Unconventional AGN from the SDSS ................................ 247 P. Hall, G. R. Knapp, G. T . Richards, M . A. Strauss, F. Anderson, D. P. Schneider, D. A. Vanden Berk, D. G. York, K. S. J. Anderson, J. Brinkmann and S. A . Snedden X-ray Evidence for Multiple Absorbing Structures in Seyfert Galaxies 253 J . M. Gelbord, K. A. Weaver and T. Yaqoob Nonlinearity in 3C390.3 ............................................. A. Mercado and L. Carrasco A Near-infrared Perspective of hard X-ray Selected Sources with High X/O Ratios ................................................... M. Mignoli and L. Pozzetti
255
257
Observational Manifestations from Star Cluster Winds . . . . . . . . . . . . . . 259 A. Rodriguez-Gonza'lez, S. Silich and G. Tenorio-Tagle
xiii
Spectral Energy Distribution Spectral Energy Distributions (SEDs) of Quasars and Active Galactic Nuclei (AGN) .............................................. B. J . Wakes X-ray Weak AGNs: Absorption or an Intrinsically Different SED? G. Risaliti, M. Elvis and E. Memola
263
. . . 275
Infrared SEDs of Quasars & Radio Galaxies: Unification and Dust Evolution Seen by ISO, SCUBA and MAMBO ...................... M. Haas
281
The z > 4 Quasar Population Observed by Chandra and XMM-Newton ...................................................... C. Vignali, W. N. Brandt and D. P. Schneider
287
A Composite EUV AGN Spectrum and the AGN Contribution to the Low Redshift UV Background ........................... J. Scott, G. Kriss, M. Brotherton, R. Green, J. Hutchings, J. M. Shull and W. Zheng BL Lac X-ray Spectra: Simpler than We Thought E. Perlman et al.
291
................... 295
Spectral Energy Distribution in the UV-X Ray Region of Two Quasars ....................................................... S. A . R. Haro-Corzo, L. Binette, E. Benitez, M. Rodriguez-Martinez and Y. Krongold Radio, FIR, Optical and X-ray Properties of NLSls and NLQSOs from the SBS ....................................................... E. Benitez, I. Cmz-Gonzalez, J. A . Stepanian, V. Chavushyan and R. Mujica
299
303
First Results from a Multi-wavelength Survey of Quasar Jets . . . . . . . . 305 J. M. Gelbord The X-ray Properties of the PG QSO Sample Observed with XMM-Newton ...................................................... E. Jiminez, E. Piconcelli, M. Guainazzi and N. Schartel
307
Nuclear SEDs of a Sample of Nearby Seyfert Galaxies ............... 309 F. Panessa, L. Bassani, M. Cappi, M. Dadina and K. Iwasawa
xiv
Search for Radio Quiet BL Lacertae Objects ........................ T. Pursimo, T. Rector, M. Tornikoski and D. Londish
311
X-ray Sources and a Radio Source in a Faint Mid-Infrared Sample . . . 313 Y. Sat0
Luminosity Functions, Evolution and Contribution to the Cosmic Background X-ray Luminosity Functions of Active Galactic Nuclei ............... 317 T. Mayaji The Missing X-ray Background ..................................... A . Comastri Active Galactic Nuclei in the Mid-IR. Evolution and Contribution to the Cosmic Infrared Background ................................. F. La Franca and I. Matute
323
329
Bridging the Cosmic Infrared Background to the X-ray Background . 335 L. Silva, R. Maiolino and G. L. Granato Cosmological Evolution of the Hard X-ray AGN Luminosity Function 339 Y. Ueda, M. Akiyama, K. Ohta and T. Miyaji CENSORS: The VLT/VLA mJy Source Survey for High Redshift AGN Evolution ..................................................... M. Brookes and P. N . Best
343
10 Years of BL Lac Selection: What Have We Learnt? . . . . . . . . . . . . . . 347 M. M. J. Marcha" Intermittency, Accretion Disks and AGN Evolution . . . . . . . . . . . . . . . . . 351 A . Siemiginowska, A . Janiuk, B. Czerny, M. Sobolewska and R. Szczerba BL Lac Evolution Revisited ......................................... A. Wolter, F. Cavallotti, J. T. Stocke and T. Rector
353
The Resolved X-ray Background in the Lockman Hole . . . . . . . . . . . . . . 355 M. A . Worsley, A . C. Fabian, S. Mateos, G. Hasinger and H. Brunner
xv
AGN-Galaxy Coevolution and Relic Black Holes Connection of QSOs with Local Massive Black Holes . . . . . . . . . . . . . . . . 359 Q. Yu The Host Galaxies of 23,000 AGN .................................. T. M. Heckman and G. Kauffmann
365
....................
373
Quasar Host Galaxies: Recent Results from HST M. Kukula
A Physical Model for the Joint Evolution of QSOs and Spheroids . . . 379 G. L. Granato, L. Silua, L. Danese, G. De Zotti and A . Bressan Black Hole Masses of High-redshift Quasars M. Vestergaard
.........................
385
The Cosmological Evolution of Quasar Black-Hole Masses . . . . . . . . . . . 389 R. McLure and J. S. Dunlop Accreting a t the Eddington Limit W. J . Duschl
...................................
393
BVRI Surface Photometry of Mixed Morphology Pairs of Galaxies: Interactions, Mergers and Nuclear Activity ..................... A . Franco-Balderas, D. Dultzin-Hacyan and H. M. Herncindez- Toledo Study of Stellar Populations in Interacting Systems of SBS Galaxies .................................................... A , Franco-Balderas, E. Benitez and J. A . de Diego GOODS AGN Host Structural Parameters and Environment: Evidence for Black Hole-bulge Correlation and Against Merger-AGN Connection a t z -0.4-1.3 .......................... N . A . Grogin, C. J. Conselice, E. Chatzichristou Explaining Low Redshift Quasar Evolution A . Steed and D. H. Weinberg
.......................
Determination of Nuclear SB Ages in Seyfert Galaxies ........... J . P. Torres-Papaqui, R. Terleuich and E. Terlevich
395
. . . 397
. . . 399 ... 40 1 403
xvi
AGN and Large Scale Structures Large-Scale Structures in the Chandra Deep Fields .................. 407 R. Gilli New Results on the AGN Population in Clusters of Galaxies . . . . . . . . 413 P. Martini, D. D. Kelson, J. S. Mulchaey and A. Athey The Triggering and Bias of Radio Galaxies .......................... K. Brand, S. Rawlings, J. Tuftsand G. J. Hill
417
AGN Activity in High Redshift Clusters and Protoclusters .......... 421 0. Johnson, P. Best and 0. Almaini The Clustering of XMM-Newton Hard X-ray Sources ................ 425 M. Plionis, S. Basilakos, A. Georgakakis and I. Georgantopoulos The Search for AGN in Distant Galaxy Clusters .................... R. Dowsett, 0. Johnson, P. N . Best and 0. Almaini
429
Large-Scale Radio Structure in the Universe: Giant Radio Galaxies . 431 M. Jamrozy, U. Klein, J. Machalski and K.-H. Mack High-Redshift Lya Forest Lines in a Concordance ACDM Universe . . 433 J. Wagg, A. Babul, R. Davi, S. Ellison and A . Songaila Author Index
435
Preface The Guillermo Haro 2003 Conference on Multiwavelength A GN Surveys was held in Cozumel, Mexico, from the 8th to the 12th of December 2003. 120 scientists from 15 different countries attended the meeting. The conference was conceived to give a broad overview of the recent results obtained from major AGN surveys over the whole electromagnetic spectrum. Some of the topics which were discussed during the meeting are: AGN evolution, contribution to the cosmic background, AGN luminosity functions in different wavebands, multiwavelength properties of AGN, unified model and unconventional AGN, co-evolution of AGN and galaxies, implications for the local density of supermassive black holes, and future AGN surveys planned with forthcoming observational facilities. Some of the results presented at the conference were obtained during the 8th Guillermo Haro workshop, held at INAOE in June-July 2003. Both the conference and the workshop were certainly fruitful and generated many new ideas. We are grateful to the Board of Directors of the Guillermo Haro Program in Astrophysics for giving us the opportunity to organize these two events. This volume reflects the material under discussion at the meeting that was divided in two parts, the first one dedicated to recent surveys a t all wavelengths, from radio to X-rays, and the second to the results obtained from them. We thank the members of the Scientific and Local Organizing Committees for their contribution to the organization of this meeting. We are grateful to the Guillermo Haro Program Secretary, R. Sanchez, to G. Ceron and P. Tecuatl for their efficient work on the logistics, and to the INAOE graduate students, all of them helped us to have an untroubled conference. Our warmest thanks go to INAOE for sponsoring this workshop and conference through the Guillermo Haro Program. We gratefully acknowledge the help of CONACyT through the Cooperacih Internacional office and grant 5-321783. We also acknowledge partial financial support from the Italian Institute for Astronomy (INAF) and from the Italian Ministry for Research (MIUR). Special thanks to the Osservatorio di Arcetri where the final edition of the proceedings was achieved. The Editors Ralil Mlijica & Roberto Maiolino xvii
Part I. AGN Surveys
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X-ray Surveys
44
A LONG, HARD LOOK AT THE X-RAY BACKGROUND THE CHANDRA DEEP FIELDS
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F. E. BAUER Institute of Astronomy, Madingley Rd., Cambridge, CB3 OHA, UK E-mail:
[email protected] We briefly review some of the basic properties of the Chundru Deep Field (CDF) Xray sources, explore the CDF X-ray number counts for both AGN and galaxies and how they contribute to the X-ray background, and highlight a few recent results regarding the host-galaxy morphologies of the CDF AGN using HST ACS data.
1. Introduction
Observations of the Chandru Deep Fields-North and -South (hereafter CDFN and CDF-S, or combined as CDFs) have resolved the vast majority of the X-ray background (XRB) below 223 keV [14]. Focus has now shifted toward quantifying the nature of the resolved sources, which are believed to be dominated by Active Galactic Nuclei (AGN). The two legacy CDFs stand to offer some of the best insights in this regard because of their excellent multi-wavelength data. In addition t o deep X-ray, they have deep HST, SIRTF, radio, and ground-based optical imaging, as well as several thousand spectroscopic redshifts. In this proceeding, we briefly review the basic properties of the CDF X-ray sources, break down the CDF X-ray number counts by source type, and look at the morphologies of the host galaxies of the CDF AGN using recent HST ACS data. 2. X-ray Source Properties and Source Diversity
Our sample is derived from the catalogs of Ref. 3, which consist of 503 Xray sources in the 2 Ms CDF-N and 326 X-ray sources in the 1 Ms CDF-S. Optical magnitudes for the sources have been measured using Subaru observations in the CDF-N [6] and Wide-Field Imager ( W I ) observations in the CDF-S [4],while redshifts were gathered from several recent catalogs [6, 12, 17, 18, 201. Of the 829 CDF sources, 425 have spectroscopic redshifts and 80 have firm photometric redshifts. Most sources with known redshifts have 5
6
R < 24 and can often be securely classified as AGN based on either their Xray luminosities/spectra/variability, radio properties, optical spectroscopic classifications, or X-ray-to-optical flux ratios [2, 51. Classifications of the R > 24 sources, however, typically remain ambiguous because they lack firm redshifts and their X-ray properties are consistent with emission from either a low-luminosity active nucleus, star formation, or a combination of both. Figure 1 compares R-band magnitude and redshift. Notably, the majority of the CDF sources appear to be better matched to L* galaxy spectral energy distributions (SEDs) than to a QSO/AGN SED, implying that those CDF sources that are AGN are probably obscured at optical wavelengths [l].The good correspondence between optical magnitude and redshift suggests we can use R as a crude redshift indicator to glean basic trends. Estimating the remaining CDF redshifts in this manner, we classified the CDF sources into Galactic stars, AGN (fo.5--8.0 k e v / f ~> 0.1, N H 2 cm-', erg s-l, or broad/high-ionization band ratio > 0.8, Lo.5--8.0 keV > 3 x AGN emission lines), and star-forming galaxies (the remaining sources). These samples are used below.
3. X-ray Number Counts
Figure 2 presents the CDF logN-logs in the 0.5-2.0 keV and 2-8 keV bands. The number counts have been corrected for incompleteness and flux bias using Monte Carlo simulations. The number counts are shown for all sources, as well as separately for AGN, galaxies, and stars. The total CDF log N-log S curves are consistent with the models of Ref. 14. Maximumlikelihood fitting of the differential number counts yielded best-fit slopes to the total faint-end number counts (< 2 x erg cmP2 s-l in each band) of 0.51f0,:;6, (0.5-2.0 keV) and 0.44'0,::; (2-8 keV). Split among our three source types, it is clear that AGN continue to dominate the number counts in both bands, although the number counts of star-forming galaxies are rapidly rising [with slopes of 1.24?0,:$ (0.5-2.0 keV) and 2.11!0,:6,2, (28 kev)] and in terms of sky density they should become more numerous than AGN just below the current 2 Ms CDF-N sensitivity limit. Using total X-ray background (XRB) flux densities of (7.52 f 0.35) x erg cm-2 s-l deg-' (0.5-2.0 keV) [14] and (2.24 f 0.11) x erg cm-' s-l deg-2] (2-8 keV) [8] and adopting the model of Ref. 14 to account for sources brighter than 1 x erg cm-2 s-l in both bands, we find that 89.5t::: and 86.9f6,:: per cent of the XRB is resolved in the 0.5-
7
2
80 60 40 20 0 6
5 4 4 c
2 m 'CI 0
3
p:
2 1 n "
16
18
20
22 24 R (mag)
26
28
0 2040 60 80
N
Figure 1. The R-band magnitude versus redshift distribution for all 829 CDF sources, along with typical L' QSO and galaxy SEDs. The sources with known redshifts have additionally been subdivided into spectroscopically ( 2 ) and photometrically (PHOT 2 ) identified objects, as well as those with broad emission lines (BLAGN). Redshifts for sources that lacked them were estimated based on an Sb galaxy SED (EST. 2). Also shown are the corresponding R-band and redshift histograms to illustrate the underlying distributions. The 52 sources with R > 27 (dotted histogram in the R-band magnitude distribution) were assigned R-band magnitude assuming they represent the tail of the currently observed distribution; some sources could be much fainter than our estimates. The dashed curve in the redshift histogram indicates the expected distribution of AGN measured from ROSAT observations, normalized to the total number of AGN in the CDFs (assumed to be ~ 8 0 % of all CDF sources).
2.0 keV and 2-8 keV bands, respectively. While extrapolation of the total number-count slopes (only an additional ~ 2 - 3per cent) cannot account for all of the remaining 0.5-2.0 keV and 2-8 keV XRBs, extrapolation of the galaxy number-count slopes alone can plausibly account for the remaining XRB to within errors. We caution that these results ignore possible large-scale structure effects and instrumental cross-calibration uncertain-
8
Figure 2. The soft (left) and hard (right) number counts in the Chandra Deep Fields are shown for all sources (solid black curves) and three different X-ray subsets: AGN (dashed grey curves), galaxies (solid dark grey curves), and stars (thick solid black curves). Also shown are the best-fit X-ray number counts models of Ref. 14 (thin solid black curves), the 1 Ms CDF-N fluctuation analysis results from Ref. 13 (grey “fishtails”), and the predicted X-ray counts of star-forming galaxies from Ref. 15, calculated assuming the X-ray/radio correlation [5, 151 and the total radio number counts of Ref. 16 (thin dotted grey lines). The percentage of the XRB resolved at a given X-ray flux (calculated from the number count models of Ref. 14, although renormalized in hard-band to the total hard XRB flux density of Ref. 8) is shown at the top of the panels.
ties, which could be as large as ~ 1 0 - 2 0 %[8]. At the CDF flux limits, we find AGN source densities of 7166+3,:; sources deg-2 (0.5-2.0 keV) and 4558tiA6, (2-8 keV), which are factors of 10-20 higher than the 300-500 sources deg-2 found in the deepest optical AGN surveys [lo, 19, 111. Thus optical observations appear to be missing >90% of AGN compared to the deepest X-ray observations, although a direct comparison is not entirely fair since optical surveys often target specific redshift and luminosity ranges. X-ray and optical survey results are more consistent when compared within these ranges [ l l ] . Importantly, deep optical surveys generally pick out AGN with strong emission lines ok blue continua, while X-ray observations appear to be far more effective at finding typical Type 2 AGNs. This conclusion is not entirely surprising given that t1.e optical spectra of many AGN in the CDFs are dominated by hostgalaxy light. Caution should be exercised when using the above values, however, since a large number of Compton-thick AGN, which are thought
-
9
to comprise perhaps -50% of all AGN, are almost certainly missing.
Figure 3. H S T combined BViz’ postage-stamp images (6” x 6 ” ) showing the host galaxies of the most luminous AGN with z < 1.3 in the 2 Ms CDF-N. Images shown in descending Lo.s-s.0 keV order. A “B” in the upper left corner denotes a broad-line AGN (typically the most luminous AGN), while the lower left corner provides, in descending order, our AGN classification, X-ray ID number from Ref. 3, intrinsic Lo.~-s.okeV, spectroscopic redshift, and z’ magnitude.
4. AGN Host Galaxy Properties
The extensive multi-wavelength ancillary data for the CDFs includes HST ACS BViz imaging as part of the Great Observatories Origins Deep Survey (GOODS; [9]). These data provide some of the deepest and highest-quality optical imaging t o date, and allow unprecedented morphological classification of the CDF AGN. Figure 3 presents greyscale postage-stamp images for a small sample of the CDF AGN. Concentration and asymmetry measurements [7] for these AGN, as well as optical colors, indicate that their host galaxies are evenly split between ellipticals and spirals. This suggests that the CDF X-ray sources, which represent the bulk of XRB, are not simply QSOs going through secondary emission phase since this would imply a purely elliptical distribution. Finally, compared to the field galaxy population with M B < -19.5 and z < 1.3, the CDF AGN hosts are preferentially
10
associated with more concentrated galaxies (implying they may be more bulge-dominated) but show no difference in asymmetry (implying they are probably not powered by mergers); see conference contribution by Grogin et al. These studies highlight how the recent HST data may help us better understand AGN evolution. 5 . Future Prospects
The CDFs will likely remain at the observational forefront for understanding faint X-ray AGN. Importantly, deep SIRTF observations are scheduled throughout 2004 to provide strong mid-IR constraints on the X-ray selected AGN and the possibility of detecting additional, highly-obscured AGN which may be missed by the current X-ray observations; see conference contribution by Treister et al. Deeper radio and near-IR imaging, as well as expanded SCUBA coverage are also planned, and should offer stronger constraints on the nature of the AGN host galaxies and/or AGN spectral energy distributions. Finally, additional X-ray observations are underway/proposed to expand the areal coverage of the CDF-S and probe even deeper in the CDF-N.
References 1. D. Alexander et al., AJ 1 2 2 , 2156 (2001). 2. D. Alexander et al., ApJL 5 6 8 , L85 (2002). 3. D. Alexander et al., A J 126, 539 (2003). 4. S. Arnouts et al., A&A 3 7 9 , 740 (2001). 5. F. Bauer et al., A J 1 2 4 , 2351 (2002). 6. A. Barger et al., A J 1 2 6 , 632 (2003). 7. C. Conselice, A p J S 1 4 7 , 1 (2003). 8. A. DeLuca & S. Molendi, A&A in press, (2004). (astro-ph/0311538) 9. M. Giavalisco et al., ApJL 6 0 0 , L93 (2004). 10. P. Hall et al., AJ 120, 2220 (2000). 11. M. Hunt et al., A p J 6 0 5 , 625 (2004). 12. 0. Le Fevre et al., A&A in press, (2004). (astro-ph/0403628) 13. T. Miyaji & R. Griffiths, ApJL 5 6 4 , L5 (2002). 14. A. Moretti et al., ApJ 5 8 8 , 696 (2003). 15. P. Ranalli, A. Comastri & G. Setti, A&A 3 9 9 , 39 (2003). 16. E. .A. Richards, A p J 5 3 3 , 611 (2000). 17. G. Szokoly et al., ApJS in press, (2004). (astro-ph/0312324) 18. G. Wirth et al., A J in press, (2004). (astro-ph/0401353) 19. C. Wolf et al., A&A 4 0 8 , 499 (2003). 20. C. Wolf et al., A B A in press, (2004). (astro-ph/0403666)
HIGH ENERGY LARGE AREA SURVEYS AND THE HISTORY OF ACCRETION IN THE UNIVERSE *
F. FIORE' AND THE HELLAS2XMM COLLABORATION INAF-Osservatorio Astronomic0 d i Roma , Italy via Rascati, 33, 1 0 0 0 ~ 0 Monteporzio, E-mail:
[email protected] Hard X-ray, large area surveys are a fundamental complement of ultradcep, pencil beam surveys in obtaining a more complete coverage of the L-z plane, allowing to find luminous QSO in wide z ranges. Furthermore, results from these surveys can be used to make reliable predictions about the luminosity (and hence the redshift) of the sources in the deep surveys which have optical counterparts too faint to be observed with the present generation of optical telescopes. This allows us t o obtain accurate luminosity functions on wide luminosity and redshift intervals.
1. Introduction
Hard X-ray surveys are the most direct probe of super-massive black hole accretion activity, which is recorded in the cosmic X-ray background (CXB) spectral intensity. Deep, pencil beam, Chandra and XMM-Newton surveys have resolved most of the CXB below 4-6 keV, and M 50% of the CXB at 10 keV (Worsley et al. 2004). The optical spectroscopic follow-up of the Chandra Deep Field North/South (CDFN, CDFS) and of the Lockman Hole (LH) surveys proved to be very efficient a t identifying a large population of Seyfert-like objects up t o z=2-3, and a few QSOs up t o z=4 (see Fig. l a and references in Table 1). Shallower, but larger area surveys are therefore fundamental to: a) complement the pencil-beam survey to obtain a more complete coverage of the L-z plane, to find QSO with logL(2-1OkeV)>44, i.e. close to AGN luminosity function L*, in a large z range; b) to obtain reliable spectroscopic redshifts of the faint optical counterparts of sources with X-ray to optical flux ratio (X/O) much higher than that of typical broad line AGN (X/O- l),which make 20-30% of the full samples. At the *This work is partially supported by AS1 grant i/r/057/02, by INAF grant # 270/2003 and MIUR grant cofin-03-02-23
11
12
10-100 times fainter fluxes reached by the CDFN, CDFS and LH surveys most sources with high X/O have optical counterparts too faint for even 810 m class telescopes. The best hope to obtain information on this elusive X-ray source population is to make use of the information gained at higher fluxes to make reliable predictions about their luminosities and redshifts. 1.1. Source samples
Figure l b) compares the fluxes and area covered by a number of hard X-ray surveys, In this paper we use the source samples given in Table 1, which include the deepest surveys performed with Chandra and the shallower, but much larger area HELLASBXMM survey. As of today we have obtained spectroscopic redshifts for more than 150 sources, and, most important, we were able to obtain spectroscopic redshifts and classification of many sources with X/O> 10; finding about ten type 2 QSO at z=O.7-2, to be compared with the similar number obtained from the combination of the CDFN and CDFS, a t the expenses of a huge investment of VLT and Keck observing time. For other 8 X/O> 10 sources a redshift estimate was obtained from their observed R-K colors (Mignoli et al. 2004). Sample HELLASBXMM CDFN fainta CDFN brightb CDFS fainta CDFS brightb Lockman HoleC SSA13d
Tot. Area deg2
Flux limit cgs
# sour.
z-spec
ref
symbol
1.6 0.0369 0.0504 0.0369 0.0504 0.126 0.0177
8.0 1.0 3.0 1.0 3.0 4.0 3.8
231 88 44 68 55 55 20 561
66% 59% 65% 62% 58% 75% 65% 65%
1.2 3,4 3,4 5,6 5,6 7 8
open circ. filled squar. filled squar. stars stars filled triang. filled circ.
Total
Note: a Inner 6.5 arcmin radius; outer 6.5-10 arcmin annulus; inner 12 arcmin radius; inner 4.5 arcmin radius; (1) Fiore et al. 2003; (2) Cocchia et al. in prep.; (3) Alexander et al. 2003; (4) Barger et al. 2003; (5) Giacconi et al. 2002; (6) Szokoly et al. 2004; (7) Mainieri et al. 2002; (8) Barger et al. 2001.
2. Optically obscured AGN: a robust method to estimate
their luminosity Fiore et al. (2003) discovered a striking correlation between X/O and the 2-10 keV luminosity for the sources with the nucleus strongly obscured in the optical band, i.e. not showing broad emission lines (Fig. 2a). The dispersion along the correlation in Fig. 2a) is of 0.40 dex in luminosity. Note
13 100
10
bu
P
g
1
U
0
1
2 Redshift
3
4
,o-,e
10-14 1043 2-10 keV Flux cgs
10-~6
Figure 1. Left: The L(a-lOkeV)-z plane for the source samples in Table 1 (symbols as in Table 1). The lower (upper) solid (dashed) lines represent the flux limits of erg cm-2 s-l (i.e. HELerg cm-’ s-l (i.e. Chandra deep surveys) and LAS2XMM survey) respectively. Right: The flux-area diagram for several 2-10 keV surveys. Open triangles = Chandra surveys, filled triangles = XMM-Newton surveys, stars = Chandra or XMM-Newton “contiguous” mosaics
as at X/O 2 10 most of the sources are from the HELLAS2XMM sample, i.e. it is mostly thank to this sample that it is possible to extend and validate the correlation at high X/O values, and therefore at high luminosities. From X/O, and hence the luminosity, it is possible to estimate the redshift of optically obscured sources. We call the resulting redshift estimates “Xphoto-z” . Fig. 2b) plots our X-photo-z against the spectroscopic redshifts. The correlation is again rather good and a ( A z / ( l f z ) 0.2). This can be compared with the value of 0.1, typical of accurate “photometric” redshift estimates. We note that in our case only 2 bands are used, against the several 0-NIR bands necessary to obtain reliable photo-z. Our present X-photo-z estimates are obtained using a linear fit to the logX/O-logL(21OkeV) relationship. More accurate estimates can be obtained using higher order polynomials (Fiore et al. 2004 in prep.). N
N
2.1. Optical us X-ray obscuration: the “Figure of Merit” Perola et al. (2004) found that most type 2 AGN in the HELLAS2XMM sample have significant obscuration (rest frame absorbing column NH > loz2 cm-’) also in the X-rays. Perola et al. (2004) and Comastri & Fiore (2004) also found a good correlation between X/O and NH. Both facts suggest that X-ray sources logNH > 22 are likely to be also optically ob-
14 I
'
'
"'-1
' "fl
1W
d
c 0 n x
0.1
0.01
Lag Luminosity (2-10 keV) erg
8-1
Figure 2. Left: the X-ray to optical ratio as a function of the X-ray luminosity for 123 optically obscured AGN with secure redshift and classification from the samples in Table 1. The three solid lines are the least squares fit of y=y(x) and x=x(y) and their average. Right: Spectroscopic redshift versus the redshifts evaluated using the correlation in the left panel and the X-ray flux.
scured AGN. However, for many weak sources in the samples in Table 1, N H proper spectral fits are unfeasible and a rough spectral information can be derived from their softness ratio only. The correlation between the softness ratio and N H is reasonably good (Perola et al. 2004) and therefore using the former to select X-ray obscured AGN is not a bad approximation. The relationship between X-ray obscured AGN and optically obscured AGN is not one to one. This is clearly seen in Fig. 3b), which shows that 90% of type 1 AGN have (S-H)/(S+H)> -0.5 (i.e. most of them have a soft spectrum) and 70% of optically obscured AGN have (S-H)/(S+H)< -0.5 (i.e. the majority have a hard, likely obscured spectrum, but 30% have a soft spectrum). This means that using a single (S-H)/(S+H) threshold to decide whether an X-ray source with a faint optical counterpart is an optically obscured AGN has an intrinsically large uncertainty. For this reason, we instead compute for each source a "figure of merit" (FoM, Fiore et al. 2004 in prep.), using: 1) the X/O ratio and the fraction of obscured/unobscured sources as a function of X/O (see Fiore et al. 2003); 2) the morphology of the optical counterpart, i.e point-like sources are likely to be optically unobscured sources; 3 ) the probability distribution of the softness ratio for obscured and unobscured AGN, as estimated for the sources with spectroscopic redshift and classification in Table 1. If a source has a FoM qualifying it as optically obscured we use the correlation in Fig. 2a) to estimate its redshift; if a source qualifies as an optically unobscured AGN we guess its
-
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15
redshift using the loose relation between X-ray flux and redshift for type 1 AGN. These estimates should therefore be considered in a statistical sense only (Fiore et al. 2003). At fluxes lower than erg cmP2 s-l only M 30% of the sources qualify as unobscured AGN.
40
30
20
10
0 -I
-0.5 0 Softness Ratio S-H/S+H
0
1
2
3
4
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Redshift
Figure 3. Lef3:The distribution of the softness ratio of optically obscured and unobscured sources. Right:The evolution of the number density of hard X-ray selected AGNs in three luminosity bins. The solid curve represents the evolution of optically selected QSO with M g 5 - 24. The three dashed curves are predictions from Menci et al. 2004
3. The evolution of hard X-ray selected sources Once redshifts and luminosities of the sources of the full sample are known (either spectroscopically measured or photometrically and statistically estimated) we can compute the luminosity function of hard X-ray selected sources and its redshift evolution. Fig.3b) plots the AGN number density in three luminosity bins as a function of z. This is compared with the number density of luminous optically selected QSOs and with the prediction of the Menci et al. (2004) semi-analytic, hierarchical clustering model (MM). While the density of luminous AGN increases monotonically up to ZN 3, following the evolution of optically selected AGN, and in agreement with the MM, the evolution of increasingly lower luminosity AGN peaks at decreasingly lower redshifts. The peak redshifts are also lower than those of the MM predictions. At z > 1 - 2 the density of logL=44 - 44.5 AGN decreases sharply, and it is inconsistent with the MM predictions, while the density of logL< 44 AGN is not well constrained by the present data. An extension of the present analysis to flux limits lower than those in Table 1, and therefore to higher z, is in progress (Fiore et al. 2004 in prep.). The
16
paucity of Seyfert-like objects a t z > 1 - 2 can be due to at least two reasons: a) a selection effect, i.e. highly obscured AGN are common a t these redshifts (as in the nearby Universe) but are missed (or their luminosity is underestimated) in Chandra and XMM-Newton surveys (La F'ranca et al. 2004 in prep.); b) a different description of the mechanisms regulating the amount of cool gas in low-mass host galaxies, the physical mechanism at work a t small accretion rates and/or the statistics of DM condensations is needed in the MM. To avoid possible selection effect, for an unbiased census of the AGN population making the bulk of the CXB and an unbiased measure of the AGN luminosity function a t z=1-2, the "golden epoch" of galaxy and AGN activity, sensitive observations extending at energies where photoelectic effect no more reduces the observed flux (i.e. E> 10 keV) are clearly needed. More specifically to resolve -50% of the 20-100 keV CXB we need to go down to fluxes of erg cm-2 s-l in this band (see fig. 6 of Menci et al. 2004). This can be achieved only by imaging X-ray telescopes, possibly with multi-layer coatings (see e.g. Pareschi & Cotroneo 2003). Key issues are: a) high collecting area; b) sharp PSF (15 arcsec or less Half Energy Diameter, HED); c) low detector internal background.
Acknowledgments The original matter presented in this paper is the result of the effort of a large number of people, in particular of the HELLASZXMM team (A. Baldi, M. Brusa, N. Carangelo, P. Ciliegi, F. Cocchia, A. Comastri, V. D'Elia, C. Feruglio, F. La Franca, R. Maiolino,
G. Matt, M. Mignoli, S. Molendi, G. C. Perola, S. Puccetti, C. Vignali, N. Menci, A. Cavaliere, M. Elvis and P. Severgnini.
References D.M. Alexander et al., AJ 126,539 (2003). A . Barger et al., AJ 126,632 (2003). A. Barger et al., AJ 121,662 (2001). A. Comastri & F. Fiore (2004). (astro-ph/0404047) F. Fiore et al., A&A 409,79 (2003). R. Giacconi et al., ApJS 139,369 (2002). V. Mainieri et al., A&A 393,425 (2002). 8. N. Menci et al., ApJ 606,58 (2004). 9. M. Mignoli et al., A&A 418,827 (2004) 10. G. Pareschi & V. Cotroneo, SPIE Proc. 5156 (2003) 11. G.C. Perola et al., A&A in press (2004). (astro-ph/0404044) 12. G.P. Szokoly et al., A p J in press (2004). (astro-ph/0312324) 13. M.A. Worsley et al., MNRAS submitted (2004). (astro-ph/0404273)
1. 2. 3. 4. 5. 6. 7.
X-RAY SPECTRA OF XMM-NEWTON AGN FROM MEDIUM AND DEEP SURVEYS *
S. MATEOS, X. BARCONS, F.J. CARRERA AND M. T. CEBALLOS Instituto de Fisica de Cantabria (CSIC-UC) 39005 Santander, Spain E-mail: mateosQifca.unican. es
We present the results of a detailed X-ray spectral analysis of a large sample of medium-faint-flux sources detected serendipitously with the XMM-Newton observatory. We also show the preliminary results of a similar study that we are conducting on the brightest sources detected with XMM-Newton in a deep exposure of the Lockman Hole field.
1. X-ray spectra of XMM-Newton serendipitous sources
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For this study we used 25 XMM-Newton observations selected from the public data archive, covering a total solid angle of 3.5deg2. The selected fields are being followed-up in the optical band as part of the XMM-Newton Survey Science Centre identification programme (XID) a~tivities.~.We selected observations at high Galactic latitudes (lbl > 20deg), and the XMM-Newton European Photon Imaging Camera (EPIC)-pn used in full window mode to search for the sources. The source detection algorithm (SAS v5.3.3. eboxdetect-emldetect) was run for each observation on pn data and on the five standard XMM-Newton energy bands (0.2-0.5, 0.5-2.0, 2.0-4.5, 4.5-7.5 and 7.5-12.0 keV) simultaneously. The objects with a total detection likelihood of more than 10 were included in the final list of sources. The total number of sources detected was 2018. At the moment, 210 (12%) sources in our list have been identified through optical spectroscopy, the majority (149) being Broad Line AGNs (BLAGNs). We have also 32 Narrow Emission Line Galaxies (NELGs) *This work was supported in part by the German BMBF under DLR grant 50 OX 0201. t SM acknowledges support from Universidad de Cantabria fellowship. XB,FJC and MTC acknowledge financial support from the Spanish Ministerio de Ciencia y Tecnologia, under project ESP2003-00812.
17
18
and 10 absorption line galaxies (ALG). For each detected object we have extracted its spectral products (source and background spectra and the corresponding calibration matrices, ARF and RMF). The MOSl and MOS2 spectra were combined. We did not merge MOS and pn data due t o their very different responses. In order to allow the x2 minimization technique in the fitting process, the spectra were binned with a minimum of 10 counts (source+background) per bin. We imposed a minimum spectral quality to the grouped spectra: a number of bins (MOS+pn) 2 5, and a number of (background subtracted) MOS+pn counts 2 50. This quality filtering resulted in a final sample of 1137 X-ray sources (141 BLAGNs, 29 NELGs and 7 ALG) appropiate for spectral analysis.
Figure 1. Best fit weighted photon index versus SO.5-2.0 for the XMM-Newton serendipitous sources (left) and for the Lockman Hole sources (right). Squares for the whole sample, stars for the absorbed (F-test? 95.0%) sources and triangles for the not absorbed sources (F-test< 95.0%). Vertical error bars correspond to 90% confidence. Horizontal bars denote the flux range.
1.1. AGN X - r a y spectral properties The data were fitted with the XSPEC v11.2 software package. The sources average spectral photon index, assuming a gaussian distribution, is (r)= 1.96 f 0.01, a result in agreement with previous surveys. Absorption in excess of the Galactic value was required (F-test 2 95%) for 16-22% of the objects. Significant absorption was detected for 40-45% of the NELGs and for 6-11% of the BLAGNs (see Fig. 2). We also found that, when the spectra were all fitted with a single power law model, there was a clear dependence of the average continuum shape on the X-ray flux. Allowing the sources to be intrinsically absorbed, we still found, for the unabsorbed
19
2 o F . 0
..
.
.
.
I
I
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.
I
.
.
.
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Figure 2. Top: Distributions and redshift dependence of the BLAGNs and NELGs measured absorbing column densities. Bottom: The results obtained from a simulated input distribution of absorbing column densities (see text). The dashed histogram in the bottom-left figure represents the BLAGNs+NELGs measured distribution.
objects, the same dependence of r with the X-ray flux, as it is shown in Fig. 1. With the current data we cannot reject that these sources have the same underlying power law (I' 2) with moderate absorption, nor can we reject that there is a population with genuinely flatter spectral index3. No dependence of the sources X-ray spectral properties with luminosity and redshift (see Fig. 2) was seen. Soft excess emission was detected in 7% of the BLAGNs and NELGs ((kT) 0.17keV). Simulations have been conducted to test the distribution of absorbing column densities used in the most popular X-ray background (XRB) synthesis models (e.g. Gilli et al. 2001). For all the tested models, the number of simulated spectra where absorption was detected ( w 40%) was a factor of 2.5 above the measured values in our samples of BLAGNs and NELGs. The distributions of absorbing column densities predicted by the models are significantly skewed towards higher column densities (NH N 10" - loz4cm-'). However, these highly absorbed sources were not detected in the real sample. The spectral analysis of the 7 sources identified as ALGs, has allowed us to confirm that an AGN is the source of their X-ray emission in all the
-
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20 cases. The ALGs X-ray emission was best modelled with a single power law in 5 objects, although the flat spectral slope obtained in two of the objects does not allow us to rule out the posibility of them to be absorbed. For the other 2 objects we detected significant absorption in their X-ray spectra. 2. XMM-Newton deep survey in the Lockman Hole We are using the XMM-Newton observations of the Lockman Hole field (total exposure time of 670 ksec of pn data) to study in detail the X-ray spectral properties of the faint AGN population. We have analysed the spectra of the 104 brightest objects (the total number of detected sources is much larger), including 41 type 1 AGNs and 11 type 2 AGNs. We saw that the hardening of the average photon index obtained for the serendipitous sources is not evident in the Lockman Hole sources (see Fig. 1). This is probably because of the better quality of the Lockman Hole data, that allows to better detect the signatures of absorption in the spectra. Significant absorption was detected in 40% of the sources. Only 7 out of the 11 sources identified as type 2 AGNs are absorbed in X-rays. We have also detected significant absorption in 6 out of the 41 type I AGNs ( w 15%), see Fig. 3 N
N
Figure 3. Left: Type 2 AGN with no signatures of absoption in X-rays. Right: Type 1 AGN significantly absorbed in X-rays
References 1. 2. 3. 4.
R. Gilli, M. Salvati & G. Hasinger, A B A 366,407 (2001). S. Mateos et al., A B A submitted (2004). M.J. Page, J.P.D. Mittaz & F.J. Carrera, M N R A S 318,1073 (2000). M.G. Watson et al., A B A 365,L51 (2001).
UNVEILING THE AGN POPULATION WITH CHAMP’S X-RAY VISION
J. SILVERMAN, P. GREEN, B. WILKES, W. BARKHOUSE, D. KIM, T. ALDCROFT & THE CHAMP COLLABORATION Harvard-Smithsonian Center f o r Astrophysics, 60 Garden Street Cambridge, M A 01238, USA E-mail:
[email protected]. edu The Chandra Multiwavelength Project (ChaMP) is determining the demographics of the X-ray emitting AGN population, including those with significant obscuration. The ChaMP is providing a medium-depth, wide-area sample of serendipitous X-ray sources from archival Chandra fields covering 14 deg2. We present results from the X-ray and optical analysis of 357 AGN detected in 23 Chandra fields. The sample primarily includes broad emission line AGN (BLAGN; 53%) with a significant subset of narrow emission line galaxies (NELG; 23%) and absorption line galaxies (ALG; 11%). From X-ray spectral analysis, we report that NELG and ALG are obscured AGN ( L x > erg s-l) with an intrinsic absorbing column in the range of 1020.5 < NH < loz3.’ cmP2. These results are the first 4 with step towards measuring the X-ray luminosity function of AGN out to z the inclusion of the hidden population. N
N
1. Chandra Multiwavelength Project
The C h a n d r a Multiwavelength Project (Kim et al. 2004a; Kim et al. 2004b; Green et al. 2004) is carrying out a wide field (14 deg2) X-ray survey of the extragalactic universe. The ChaMP is a survey of serendipitous X-ray sources detected in 137 archived C h a n d r a observations. These fields probe flux levels responsible for most of the hard (2.0-8.0 keV) Cosmic Xray Background. This depth is ideal for detecting the luminous and heavily obscured AGN. The complete project expects a total of 8000 serendipitous extragalactic X-ray sources. The optical followup program (Green et al. 2004) is the backbone of the project to identify sources and measure their redshift to generate a sample 800 AGN in 40 ChaMP fields. We have acquired optical imaging (SDSS g’,r’, and 2’) for each Chandra field using the NOAO 4m telescopes with the MOSAIC camera. The use of the SDSS photometric system allows for
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22 a more direct comparison between the ChaMP and the SDSS. Optical spectroscopy is crucial for determining the source type and redshift. The majority of optical spectra are acquired from the WIYN/3.5m and CTI0/4m with HYDRA, a multi-fiber spectrograph. To extend spectroscopic classifications beyond r' 21, we have obtained spectra from Magellan and the MMT. We have been using the FLWO 1.2m to acquire spectra of the optically bright (r' < 17) counterparts. N
2 . X-ray emitting populations
We present results from the ChaMP using a sample of 1339 X-ray sources detected in the broad (0.3-8.0 keV) band in 23 fields. In these medium depth Chandra fields, we are finding a diversity of objects such as AGNs, galaxies, clusters and stars, although 85% of them are attributed to accreting supermassive black holes. We show the optical magnitude (r') as a function of 0.3-8.0 keV X-ray flux in Figure 1.
10-15
10-l~ f x (erg cm-' s-';
10-l~ 0.3-8.0keV)
10-l2
Figure 1. X-ray flux (0.3-8 keV) vs. optical magnitude (r'). Optical spectroscopic classifications are indicated (top right box). X-ray sources with no optical counterparts are shown by a n arrow placed at the hypothetical magnitude for a 50 detection from our optical imaging. T h e slanted lines mark the fx/fr ratio of O . l , l , l O
We classify each source based on its optical spectrum. Optical counter-
23 parts which have broad emission lines are labelled as BLAGN which constitute 53% of the spectroscopically identified population. Their X-ray and optical emission is correlated (Figure 1). A significant number of optically bright narrow emission line (NELG; 23%) and absorption line (ALG; 11%) galaxies are associated with faint X-ray sources. Their optical emission does not correlate with the X- ray emission suggesting that the host galaxy dominates the optical light (Green et al. 2004; Fiore et al. 2003). Many (14%) stars (i.e. M stars, LMXBs) are found at bright optical magnitudes. We have found a few X-ray emitting galaxy clusters out to ~ ~ 0 . 6 . Most studies of X-ray selected AGN rely on optical spectroscopy for further classification. This can be misleading since it’s difficult to isolate the nuclear region at these distances (Moran, Filippenko & Chornock 2002) with a 1” aperture. While most of the optical counterparts of ChaMP sources have emission lines similar to the quasars and lower luminosity Seyfert galaxies, the limited wavelength coverage can cause some confusion with source classification (Page et al. 2003). Depending on the observed wavelength range, the classification of low luminosity AGN can change drastically with the detection of broad emission lines at either the blue or red end of the spectrum. N
3. X-ray selected AGN We aim to generate a sample less biased against obscuration by using the X-ray luminosity as our primary discrimant for AGN activity. We set a threshold at L0.3-8.0kev > erg s-l to include luminous AGN such as the QSOs and Seyfert galaxies while omitting objects such as normal or star forming galaxies. In Figure 2, we plot the X-ray luminosity as a function of redshift. We find that 80% (357) of the optically identified X-ray sources (449) are AGN. A significant fraction (34%) do not have any broad optical emission lines. The steep drop in the number of NELG and ALG above Z N 0.8 is primarily due to a selection bias. A luminous galaxy (lOL,) at z ~ O . 8is fainter than our limit for optical spectroscopic followup (r’=22). In these 23 Chandra, fields, we have generated a catalog of 357 AGN to measure the X-ray luminosity function and investigate their X-ray and optical properties. cm-2) have Briefly, we find that most unabsorbed AGN (NH < optical properties characterized by broad emission lines and blue colors similiar to optically-selected quasars (Green et al. 2004; Silverman et al. in
24 I
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0.1
1 .o
I
Redshift
3.0
Figure 2. X-ray luminosity,redshift distribution. T h e horizontal, dashed line marks our chosen minimum luminosity required for AGN selection.
preparation). We have identified the absorbed AGN t o be predominantly associated with narrow emission line galaxies with column densities in the range 10" cm-') amounts of absorption. Although these present great interest for the physics of AGN, it appears that they do not form a substantial fraction of the QSO population. (iv) The spectrum of the 7 NL/AL AGN, is flatter with r 1.6. When
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28
Object type z N& Counts3 Li 3 NL 0.370 44.0 0.3?$: 153 0.145 42.8 < 0.03 95 9 NL 10 BL 0.465 43.6 34:; 39 19 BL 1.970 45.0 3;: 73 NL 0.218 42.9 < 0.4 21 56 28 AL 0.240 43.6 < 0.1 140 30 NL 2.350 45.7 < 0.6 58 AL 0.254 43.1 < 0.2 44 107 2.250 44.7 < 0.8 52 BL 34 61 NL 0.244 43.6 < 0.01 223 Logarithm of the absorbed Luminosity (0.5-8 keV) Intrinsic rest-frame column density in units of lo2' cm-' Sum of MOS and P N counts in the 0.5-8 keV band Sample All All excl. 9 bright sources BL AGN BL AGN (incl.photo-z) NL AGN NL AGN (incl.photo-z) Optically faint
No 61 52 24 30 7 18 8
r 1.832:::; 1.49::; 2.022:::; 1.98::; 1.64:::; 1.50'1:::; 1.09?::$:
X2/dof 235/238 126/132 247/151 261/165 37/32 144/75 9/8
we add t o the above, the 11 spectroscopically unidentified sources which are optically extended and present red colours, and thus are also probably associated with nearby NL AGN, we obtain a similar spectrum r x 1.5. (v) The spectrum of the 8 sources which have no optical counterpart is very flat , suggesting that these may be associated with obscured AGN a t high redshift.
References 1. W. Cash, A p J 228, 939 (1979). 2. M. Colless et al., M N R A S 328, 1039 (2001). 3. S.M. Croom, R.J. Smith, B.J. Boyle, T. Shanks, N.S. Loaring, L. Miller & I.J. Lewis, M N R A S 322, L29 (2001). 4. A. Georgakakis, I. Georgantopoulos, G.C. Stewart, T. Shanks & B.J. Boyle, M N R A S 344, 161 (2003). 5. D.G. York et al., A J 120,1579 (2000).
GALAXIES AT THE LIMIT OF DEEP X-RAY SURVEYS: GALAXIES OR AGN ?
R. E. GRIFFITHS, A.KNUDSON AND T.MIYAJ1 Physics Dept., Carnegie Mellon University 5000 Forbes Avenue, Pittsburgh, PA 15213-3890, USA E-mail:
[email protected]. edu The great sensitivities of the Chandra X-ray Observatory and XMM-Newton are allowing us to explore the X-ray emission from galaxies at moderate to high redshift. By using the stacking method, we show that we can detect the ensemble emission from normal elliptical, spiral and irregular galaxies out to redshifts approaching one. The average X-ray luminosity can then be compared with the results of models of the evolution in the numbers of X-ray binaries and can possibly be used to constrain models of star formation. In order to account for the increasing luminosity of spiral galaxies from low to moderate redshift, AGN components may need to be invoked.
1. Introduction
Deep surveys in X-ray astronomy had the initial goal of solving the problem of the origin of the extragalactic X-ray background, and these surveys have now shown that the XRB is largely comprised of the evolving populations of AGN, some heavily absorbed But the deep surveys with the Chandra X-ray Observatory (CXO) have shown that normal galaxies are also detected, and the initial 1Ms survey of the Hubble Deep Field (HDF) North demonstrated that about a third of the X-ray sources were identified with g a l a x i e ~We .~ have thus entered a new era in X-ray astronomy, one in which we can begin to explore the evolution of extragalactic source populations in addition to the AGN. 2. Deep Surveys and Source Counts
The number counts in the HDF-N have been measured by [6], and extended to fluxes below ergs cmV2s-l in the soft band (0.5 - 2 keV) and to ergs cm-2 s-l in the hard band (2 - 10 keV) by analysis of the fluctuations which remain after removal of the individual discrete source
29
30 106
0.5-2 keV
103
1
Us HDP-N Source
.
.
/.-..-..Galaxlea wlth Gaua.lsn/Peak-Y I
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,
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Figure 1. X-ray Number Counts from HDF-N
detections. Below this limit, the fluctuation analysis shows that the number counts continue t o rise, as shown in Fig. 1, with a slope consistent with that between 10-15 and 10-16 ergs cm-2 s-'. At X-ray fluxes between 10-15 and 10-16 ergs cm-2 s-', the optical identifications in the HDF-N4 show that starburst and normal galaxies begin to dominate the number counts (0.5-8 keV). We infer that the number counts in the region explored with fluctuations (the boxed area in Fig. 1) are unlikely to be due to AGN. Furthermore, the current best models for the AGN contributions t o the number counts fall well below the fluctuations. The fluctuations analysis shows that the number counts are approximately 20,000 - 40,000 per sq. deg. a t X-ray fluxes of 10-17ergs cm-2 s-'. Such number counts match those of the optical counts of galaxies a t B = 24. We therefore explore the possibility of X-ray detection of faint galaxies in the HDF-N by using the stacking method.
3. Selection of Galaxies by Morphological Type and Luminosity During the execution of the Medium Deep Survey using the Hubble Space Telescope, software was developed for the automated classification of galaxies into spirals (exponential disks), ellipticals ('de Vaucouleurs' profiles) and irregular galaxies which exhibited large residual images after the removal of disk or bulge profiles.8 This survey showed, for example, that the fraction of irregulars rises from 12% locally to 30% a t a redshift of 0.5.
31
€oft
( 0 5 - 2 0 kRV)
Figure 2. Stacked X-ray images of ensembles of galaxies
We have applied this MDS software and analysis to the HST images of the HDF-N and other deep HST surveys. In those fields where we have deep CXO observations, we can then examine the X-ray images for the presence of X-rays from the galaxies of differing broad morphological type. 4. Results of ‘Stacking’
Although the fluctuations analysis gives us an indication of the number counts of X-ray sources at the faintest flux levels currently accessible, they do not give us any indication of the nature of the sources contributing to the fluctuations. How do we find out the possible nature of these sources? One method is that of ‘stacking’, i.e. the summation of sub-images centered on objects selected at another wavelength. [2] and [4] have used this method on early CXO data of the HDF-N. In the HDF, we have the advantage of being able to use the HST images themselves to select various types of galaxies for the stacking process, using the software developed as part of the HST Medium Deep Survey.8 We have now done this for elliptical, spiral and irregular galaxies, and some of the results are shown in Figure 2. As the figure shows, the spiral and elliptical galaxies are detected at high confidence in both the soft and hard energy bands, but the irregular galaxies are detected in the soft band only. The median redshifts are 0.87 for the 27 ellipticals, 0.49 for the 54 spirals and 1.55 for the 57 irregulars in these stacked images. Monte Carlo simulations have been used to verify the statistical confidence in these results. The median X-ray luminosities (0.5 - 2 keV) are 5 x ergs s-l for the ellipticals, 6 x lo3’ ergs s-l for the spirals and 2 x lo4’ ergs s-l for the irregulars, consistent with their B-band luminosities and the average values
32 for L x / L B for the galaxy types. Typical galaxy fluxes are ergs cm-2 s-l.
N
2 - 4 x 10-l8
5 . X-ray Evolution of Galaxies
The observed X-ray evolution of spiral galaxies out t o z = 0.7 is observed to be in excess of the expected value based on the evolution of binary X-ray populations. The observed evolution is better matched with a population of AGN such that the AGN luminosity is 0.1 of the galaxy luminosity in 30% of the galaxies at z = 0.7. There are several problems which need to be solved or investigated in support of the interpretation of these results: (i) the evolution of low-mass X-ray binaries (LMXRB), (ii) the evolution of high-mass X-ray binaries (HMXRB), (iii) the evolution in the number of ultraluminous X-ray (ULX) objects and (iv) SNR and hot gas components. 6. Conclusions
Results from the stacking analysis of normal galaxy populations applied t o the CXO deep survey of the HDF-N show that normal galaxy populations are observable in these stacks out to redshifts of 1. The average X-ray fluxes observed in these stacks are consistent with the numbers and fluxes inferred from the fluctuation analysis of the CXO data. We conclude that the fluctuations are therefore caused primarily by normal galaxy populations and that such deep X-ray surveys will eventually allow us t o constrain the evolution of the binary source populations within these galaxies, using the relationship between HMXB numbers and the SFR of nearby galaxies. We have tentative evidence for the presence of AGN in some fraction of normal spiral galaxies at moderate redshift.
-
References 1. S. Anderson & B. Margon, ApJ314, 111 (1987). 2. W.N. Brandt et al., ApJ558, L5 (2001). 3 . K. Ghosh & N. White, ApJ 559, L97 (2001). 4. A. E. Hornschemeier et al., ApJ 568, 82 (2002). 5. A. E. Hornschemeier & the CDF-N team, in X-rays at Sharp Focus,ASP Conf. Series, eds. S. Vrtilek, E. M. Schlegel, L. Kuhi (2003). 6. T. Miyaji & R.E. Griffiths, ApJ 564, L5 (2002). 7. A. Ptak & R. E. Griffiths, ApJ559, L91 (2001). 8. K. Ratnatunga, R. E. Griffiths & E. J. Ostrander, AJ 118, 86 (1999).
X-RAY SPECTRAL FITTING OF AGN IN THE CHAMP*
T. L. ALDCROFT, J. D. SILVERMAN, P. J. GREEN, D.-W. KIM, W. A. BARKHOUSE, R . A. CAMERON, A. MOSSMAN AND B. J. WILKES
Harvard Center for Astrophysics, 60 Garden St., Cambridge M A 02138 E-mail:
[email protected] H. G H O S H ~AND B. J A N N U Z I ~ 'Perm State University, 2~~~~
X-ray selected AGN posess a wide range of absorption properties that challenge and broaden the concepts of AGN Unification. Objects that seem unabsorbed o p tically can show evidence for large absorbing columns in the X-rays, while heavily optically-reddened objects may show little such evidence. Most previous samples are heterogeneous both in selection and measurement. The Chandra Multiwavelength Project (ChaMP) is producing a large sample of X-ray selected AGN out to redshift 5 via deep optical followup of serendipitous sources in the Chandra archive. We have developed software which uses CIAO and Sherpa to to automatically extract ChaMP point source spectra and fit a variety of spectral models. We present the results of fitting and investigate the correlation of total gas absorption and continuum power-law index with luminosity, redshift, and spectral class. In addition to fitting each object individually, we make use of simultaneous fitting of many objects to improve the signal to noise within luminosity or redshift bins.
Using 16 fields selected from the c h a M P , l ~ ' >we ~ have created an homogeneous, well-defined sample of AGN for investigation of unified AGN models and the cosmic X-ray background. This sample was first selected based on a hard X-ray (2-8 keV) flux limit of fz > erg s-l cm-'. An extensive campaign of followup optical spectroscopy led to the positive identification of 126 sources (50% completeness), including: 67% broad emission line AGN (BLAGN), 22% narrow emission line galaxies (NALG), and 11%absorption line galaxies (ALG) with no evidence of an AGN. The *We gratefully acknowledge support for the ChaMP from NASA under CXC archival research grant AR2-3009X and NASA grant NAS8-39073.
33
34
‘4 - 0
2 Redshift
Figure 1. Possible evolution of the composite photon index for BLAGN. The error bars are 90% confidence limits.
key properties of this sample are described in the contribution by J. Silverman in this volume and in Silverman et al. 2004 (in prep). To characterize the X-ray spectral properties of the optically identified sample, we have developed a code which uses CIAO tools and Sherpa to extract an X-ray spectrum, do spectral modelling, and create fit summary files. Spectral fitting is preferred over traditional hardness ratio analyses because the results are independent of detector response, Galactic column, and source redshift. We fit three models to the data, all of which included Galactic absorption: (1)simple power-law (photon index free); (2) power-law with intrinsic absorption (photon index fixed at 1.9, intrinsic N H free); and (3) powerlaw with intrinsic absorption (photon index and intrinsic N H free). In the low-counts regime we used unbinned data with Cash statistics. Our key results are: (1) Approximately 1/2 of NELG and ALG show significant intrinsic absorption with N H > 10” cmF2; (2) Only 10% of BLAGN have detected absorption. More than 60% of non-detections have 2-a upper limits below 10” cm-’; (3) We find a sizeable sample of X-ray bright, optically normal galaxies with no X-ray absorption. Presumably there is an AGN which is completely obscured in the optical; (4) There is evidence for redshift evolution in the power-law photon index in BLAGN, as shown in Fig. 1; (5) Using simultaneous fitting of many spectra, we find that the composite BLAGN has no intrinsic absorption below redshift 1.8. References 1. P.J. Green et al., ApJS 150,43 (2004). 2. D.-W. Kim et al., ApJS 150,19 (2004). 3. D.-W. Kim et al., A p J 600, 59 (2004).
X-RAY COLOURS OF AGN IN THE 13H XMM/CHANDRA DEEP FIELD
T. DWELLY AND M. J. PAGE*
M S S L , UCL, Holmbury St. Mary, Dorking, RH5 6NT UK. email:
[email protected]. uk
We present results of a Monte Carlo analysis of the X-ray colours of sources in our very deep XMM-Newton imaging. Using detailed simulations, we test published models of the distribution of absorbing column densities against the observed data. The 2D-KS test finds that model B of [2] and the p = 8 model of 111 are preferred.
1. Introduction Optical surveys have found that the ratio, R, of obscured to unobscured AGN is approximately 4 : 1 in the local universe4. The redshift dependence of R is poorly understood because of the biases against detecting absorbed AGN in optical and soft X-ray surveys. XMM’s relatively high throughput at energies harder than 5 keV permits multi-band X-ray colour analysis to very faint fluxes. We examine published models of R by extending the single band LogN-Logs based Monte-Carlo simulation method3 to a multi-band, synthesis model based process. 2. Observations The XMM observations consist of a 200ks single pointing in an area of the sky having unusually low galactic absorption ( N H 8 x 1019cm-2). We find a total of 227 sources, at a level of certainty where we expect less than two of these detections to be spurious or confused. N
3. Simulation method
Our central assumption is that the intrinsic XLF of absorbed AGN is similar to that of their unabsorbed brethren. We extend the 0.5-2keV LDDEl *In collaboration with the XMM-OM deep field consortium
35
36 model5 t o harder energies by adding AGN absorbed by model N H distributions taken from the literature'*'. Our simulation method incorporates the effects of the XMM response, effective area, point spread function, vignetting and background to produce multi-band images. The simulated images are source-searched using the XMM-SAS task set together with a bespoke background fitting algorithm.
'-1'
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Figure 1. Colour-colour plots for model B of [2] (greyscale and contours), overlaid with values for sources in the 13h field (crosses). Contours are set to include 98%, 95% and 90% of the simulated sources. HRi = (Ri+l- Ri)/(Ri Ri+l),where R1,RzrR3,R4 are the count rates detected in the 0.25-0.5, 0.5-2, 2-5 and 5-lOkeV bands respectively.
+
4. Comparison of simulations with observational data
We use the two dimensional Kolmogorov-Smirnov test (2D-KS) t o compare hardness ratios measured in the 13h and simulated data. For HR1 vs HR2, we find that model B of [2] and the ,B = 8 model of [l]are accepted with P Z D K=~ 0.07 and 0.04 respectively, the other models are rejected with > 99% confidence. However, when we consider H R 2 vs HR3, all the models are strongly rejected with > 99.9% confidence, and do not fully reproduce the population of sources observed in the 5-lOkeV band.
References 1. 2. 3. 4. 5.
P. Gandhi & A. Fabian, MNRAS 339,1095 (2003). R. Gilli, M. Salvati & G. Hasinger, ABA 366,407 (2001). G. Hasinger et al., ABA 329,482 (1998). R. Maiolino & G.H. Rieke, ApJ454, 95 (1995). T. Miyaji, G. Hasinger & M. Schmidt, ABA 353,25 (2000).
THE SERENDIPITOUS EXTRAGALACTIC X-RAY SOURCE IDENTIFICATION (SEXSI) PROGRAM
M. E. ECKART, F. A. HARRISON, P. H. MA0 AND S. A. YOST Space Radiation Laboratory California Institute of Technology Mail Stop 220-47 Pasadena, CA 91106, USA E-mail:
[email protected]. edu
D. J. HELFAND AND E. S. LAIRD Columbia University Department of Astronomy 550 West 120th Street New York, N Y 10027, USA D. STERN Jet Propulsion Laboratory California Institute of Technology Mail Stop 169-506 Pasadena, CA 91109, USA
The SEXSI program is designed to explore the X-ray background and probe the physics of active galactic nuclei (AGN) by surveying a large area ( 2 deg2) of the 2 - 10 keV sky and by obtaining followup optical imaging and spectroscopy. The survey includes 1034 sources detected in the 2 - 10 keV band in 27 separate Chandra fields with a mean exposure time of 61 ks. Of these sources, nearly 1000 are covered by our R-band imaging and have an identified optical counterpart or a limiting magnitude thereto, allowing the determination of X-ray to optical ratios as well as providing accurate source positions necessary to plan optical spectroscopic observations. This poster includes data from 389 optical spectra of which 313 have sufficient signal and spectral features to classify the source and assign a redshift. For detailed information on survey methods, complete catalogs, and
37
Figure 1. Optical magnitude of SEXSI sources, plotted as a function of their hard-band (2 - 10 keV) X-ray flux. Where we have spectral data, sources are optically classified as either BLAGN (typical broad, high-ionization lines seen in Type 1 AGN), NLAGN (same as BLAGN but with narrower line widths of 5 2000 km s-'), ELG (narrow, lowerionization emission lines typical of gaseous nebulae), and ALG (stellar-type absorption
lines).
results, the reader is directed to the s u i t e of papers focused on the X-ray sample1, the optical imaging2, and the optical spectroscopy3.
References 1. F.A. Harrison, M.E. Eckart, P.H. M m , D.J. Helfand & D. Stern, A p J 596, 944 (2003). 2. M.E. Eckart, E.S. Laird, D.Stern, P.H. Mao, D.J. Helfand & F.A. Harrison, submitted t o A p J (2004). 3. M.E. Eckart et al., in preparation, (2004).
PRELIMINARY RESULTS FROM THE XMM MEDIUM DEEP SURVEY
L. MAR AS CHI^, M. TAJER', G. TRINCHIERI~,L. CHIAPPETTI~,L. PAIOR02, D. MACCAGN12, M. PIERRE3, J. SURDEJ4 AND 0. LE FEVRE5 I N A F Osservatorio Astronomic0 di Brera, via Brera 28, Milano, Italy, IASF via Bassini 15, Milano, Italy, C E A / D S M / D A P N I A S k v i c e d 'Astrophysique, Saclay, France, Institut d'Astrophysique et Ge'ophysique, Universite' de LiBge, Belgium, 5 L A M , Marseille, France
The XMM Medium Deep Survey (XMDS) is a joint program that involves three XMM hardware institutes (in Milan, Italy; Saclay, France; Likge, Belgium) and the VIMOS VLT Deep Survey consortium (VVDS). The project aims a t obtaining deep multiwavelength coverage of a 2 deg2 area: U, B, V, R and I images have already been obtained at a depth equivalent to IAB= 25.3,l1'>~ a radio survey has been completed a t VLA4, and a spectroscopic survey is in progress'. The X-ray band is covered by 19 XMM-Newton pointings, with a nominal exposure of 20 ksec each. In the 18 useful fields analyzed with a pipeline adapted from Baldi et al.5 (2002, ApJ 564,190) we detect 1322 sources (including multiple detections in overlapping fields) with a probability that they are a background fluctuation P< 2 x l o p 4 in at least one of the energy bands considered. They cover the flux range 10-12 < 10-16 erg cmP2 s-'. We have started a systematic investigation of the properties of the X-ray optical counterparts. We have selected a "4a" sample (i.e. 4a detection in a t least one band) in the area already covered by the VVDS: of the 338 detections, or 294 unique sources, in the flux range 2 x 10-16 - 5 x 10-13 erg cm-2 s-', -97% are detected in the 0.5 - 2 keV band; detections in the 2-10 keV band only are very few (2%), and none in the 4.5-10 keV only. This suggests that peculiar or highly absorbed spectra are not common in this sample. This is confirmed by the distribution of Hardness Ratios (Fig. l ) ,that shows only a few sources deviating from the bulk. A more quantitative study of the HR distribution is in progress. A search in the optical images in a 6" radius from the X-ray sources N
-
39
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Figure 1. Distribution of Hardness Ratios for t h e “4u” sample. Energy bands are defined as: b:0.5-2, c:2.0-4.5, d:4.5-10 keV, and HRb,=(c-b)/(c+b); HR,,j=(dc)/(d+c).
-’
Figure 2.
F(Z--lOkeV)/FR-band ratio vs F, for the “identified” sources. Horizontal lines a t f l enclose the region of classical AGNs, starbursts are a t < -1, candidate obscured AGNs a t > 1.
gives a likely identification for over 50% of the sources, either with a single counterpart or with the brightest (Amag > 3 - 4) and closest object, often ( N 1/5) also coincident with a compact radio source. Without proper spectroscopic data some ambiguity remains in associating the X-ray emission to a single object or to a group/cluster, since a significant fraction of sources appears in relatively crowded fields (N 1/4). F,/Fo ratios are plotted in Fig. 2 for the “identified” sources. The vast majority ( ~ 8 2 %lies ) in the region of the AGN population, a smaller percentage (- 11%)is in the starburst - normal galaxies range, and an even smaller percentage is in the candidate obscured AGNs region. At the time of writing we are completing the X-ray/optical association and checking on the robustness of the X-ray products (positions, fluxes and HR) before releasing the catalog to the community. N
References 1. 2. 3. 4. 5.
0. Le Fkvre et al., A&A 417,839 (2004). H.J. McCracken et al., A&A 410,17 (2003). M. Radovich et al., A & A 417,51 (2004). M. Bondi et al., A&A 403,857 (2003). A. Baldi et al., A p J 564, 190 (2002).
EXPLORING THE HARD X-RAY SKY WITH XMM-NEWTON
E. PICONCELLIl, M. CAPP12, L. BASSAN12, G. DI COCC02 AND M. D A D I N A ~ XMM-Newton Science Operation Center ( E S A ) Apartado 50727, Madrid, Spain 21ASF (Seraone d i Bologna) Via Gobetti 101 40129 Bologna, Italy E-mail:
[email protected]. es We report on a spectroscopic study of 90 hard X-ray sources observed with XMMNewton. This work provides the first step in the detailed study of the X-ray spectral properties of hard X-ray selected sources detected at faint fluxes (Fz-10 2 erg cm-' s-') near the knee of the LogN-Logs distribution. Our results illustrate well how a wide-angle survey allows population studies to be made as well as enabling tight constraints to be placed on some parameters of synthesis models of the Cosmic X-ray Background. In particular, we find for the first time that the erg cm-' s-l 1s . about a factor of fraction of absorbed sources at Fz-10 2 2 lower than expected on the basis of current synthesis models of the CXB.
1. Introduction
Our final sample consists of 90 hard X-ray sources detected in EPIC observations. To date this is the largest sample of 2-10 keV selected serendipitous sources with detailed X-ray spectral information down to F2-10 ~ 1 O - erg l ~ cmP2 s-l. Previously published works on this topic were based on hardness ratio and/or stacked-spectra analysis. Collecting suitable sources for X-ray spectroscopy our wide-angle survey addresses for the first time the analysis of each individual spectrum. The present study is therefore designed to complement at an intermediate 2-10 keV flux level the X-ray population studies made by ultra deep pencil-beam observations (see [l]for a review). Here we present a brief overview. For a full, detailed discussion, see [2]. 2. Results
In the following some of the most important results obtained in this study are reported. (a) In Fig. 1 (left) the fraction of obscured sources (i.e. with 41
42
NH 2 cmW2)found in our survey as a function of the flux in the 210 keV band is compared with the corresponding theoretical predictions of Ref. [3]; (dashed line). The mismatch between our findings and the model predictions is evident. The model indeed overestimates by a factor of 2 the fraction of absorbed sources in the range 10-14 24 mag, Type 2 AGN are the dominant population. 4. Redshift Distribution
Figure 2 shows the redshift distributions for the sources in the GOODS North and South fields (thick solid lines) compared t o the expected redshifts distributions from our model B (dashed lines). Using photometric5 and spectroscopic6 redshifts in the GOODS-S region the sample is 100% complete; however, in the GOODS North field combining spectroscopic and photometric redshifts' the sample is only 75% complete. 5 . Discussion
At redshifts z > 1, there is a clear discrepancy between the spectroscopic redshift and either the photometric redshifts or the model predictions, in the sense that there are fewer AGN with high spectroscopic redshifts. This is explained a t least in part by the effective brightness limit for spectroscopy, R < 24 mag. Obscured AGN a t z > 1 are fainter than this limit and thus are not included in spectroscopic samples. This accounts for the discrepancy between the observed redshift distribution of X-ray sources and the distribution predicted from population synthesis models for the X-ray background3.
72
- -. Model B
Figure 2. Redshift distributions for AGN in the GOODS-South (left panel) and North (right panel) fields. The observed redshift distribution (heavy solid line) which includes both spectroscopic (hatched area) and photometric redshifts and is 100%complete in the GOODS-S field and 76% complete in the GOODS-N region. The expected distribution (dashed line) calculated from the U03 luminosity function is similar but has more AGN at high redshift, especially compared to the distribution of spectroscopic redshifts.
The model predicts still more high redshift AGN than are observed in the GOODS fields. This is because the most obscured AGN will not be detected in the Chandra deep fields. Figure 2 shows a difference between the North and South fields, in the sense that there is a larger discrepancy between the photometric redshifts and the model in the North. This is due to incompleteness since the missing 25% of the AGN are preferentially fainter. The model redshift distribution is in agreement with the data once these selection effects are considered. It is also similar to the distribution predicted from population synthesis3, with the same caveat about selection effects.
References 1. D. Alexander et al., A J 122,2156 (2001). 2. A.J. Barger et al., AJ 126,632 (2003). 3. R. Gilli, M. Salvati & G. Hasinger, A&A 366,407 (2001). 4. M. Nenkova, Z. Ivezic & M. Elitzur, A p J 570, L9 (2002). 5. B. Mobasher et al., A p J 6 0 0 , L167 (2004). 6. G. Szokoly et al., in press, astro-ph/0312324. 7. Y. Ueda, M. Akiyama, K. Otha & T. Miyaji, A p J 598, 886 (2003). 8. D.E. Vanden Berk et al., AJ 122,549 (2001).
MEASURING THE LUMINOSITY DEPENDENCE OF QUASAR CLUSTERING USING THE 2DF $SO REDSHIFT SURVEY. *
N. S. LOARING, L. MILLER & 2DF QSO REDSHIFT SURVEY TEAM Mullard Space Science Laboratory, Holmbury House, Holmbury St. Mary, Dorking, Surrey, UK. E-mail:
[email protected] We have been able to accurately measure the luminosity dependence of QSO clustering independently of any redshift evolution. Contrary to the results obtained from galaxy clustering studies, we find no evidence for any luminosity segregation in the QSO population. These results suggest that local astrophysical effects play an important role in QSO formation and have important implications for models of QSO formation and evolution.
1. Introduction Observational evidence has revealed the presence of dormant super-massive back holes located in the centres of local inactive galaxies Furthermore, several studies have shown the masses of these black holes to be directly proportional to the mass of the galaxy bulge 5,4. If QSOs reside in normal galaxies then one would expect them to follow the same correlation between black hole and bulge mass. Therefore, if QSO luminosity and black hole mass are correlated this would imply a relation between QSO luminosity and bulge luminosity or equivalently bulge mass. Assuming a relation between bulge mass and host halo mass would then place more luminous QSOs in more massive haloes and we would therefore expect t o observe luminosity segregation in the QSO population as we do in the galaxy population. Here we present the results of a clustering analysis of the full 20K 2QZ catalogue, disentangling the redshift-luminosity degeneracy for the first 417.
*This work is supported by the UK PPARC.
73
74 time. A flat A cosmology ( f l = ~ 0.3, f l = ~ 0.7) is assumed throughout. 2. Correlation function analysis
-22
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1.50624 up to z ~ 6 as , expected by the classical chemical evolutionary models. However, recent models7 have shown that high iron enrichment can occur on time scales shorter than 1 Gyr. In particular, a simple model of formation of ellipticals can produce an iron enrichment peak already at 0.3 Gyr after the onset of star formation. Within the latter scenario, the high iron enrichment observed in quasars at Z-6 can be explained with a major episode of star formation, in the hosts of these QSOs, which occurred at z>9. 3. The large fraction of BAL QSOs at zw6
Broad Absorption Line (BAL) quasars are characterized by deep, broad and blueshifted absorption features associated with UV resonant lines of highly ionized species, with CIV( 1549A) generally being the most prominent. About 15% of the whole quasar population at z4.9, show broad, blueshifted CIV absorption, and are therefore BAL quasars6. This result is quite surprising when compared with the low occurrence (15%) of BALs at z4.9. The spectra of the most distant of these BAL quasars at z=6.22 (Fig. 2), is also characterized by AlIII and MgII absorptions identifying it as a LoBAL. The sample contains an additional LoBAL at ~ = 4 . 9 2 .Finding ~ 2 LoBALs out of 8 quasars is an even more surprising result, since at z4.9 are characterized by extremely deep absorption troughs (for three of them EW(CIV,b,)> l0A) indicative of large columns of gas. Although the statistics is limited, the large fraction of BAL quasars, and specifically of LoBALs, along with the deep troughs, strongly suggest that at 2-5-6, quasars are surrounded by larger amount of denser gas with respect to lower redshift quasars. Such strong outflows of dense gas are probably associated with the extreme accretion rates that characterizes
80
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1000
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Figure 2. Spectrum of the most distant BAL quasars known. Two main absorption systems are identified with “1” and “2”. The presence of AlIII and MgII absorption identify it as a LoBAL. The thin solid line is the (unreddened) non-BAL template with a slope a = -2.1. The dashed line is the average spectrum of LoBAL quasars at z 5 colour is even more intriguing2s3i4.Given the key role played by EROs in the cosmological scenario, hard X-ray observations can help to constrain the fraction of AGN among the ERO population and, at the same time, to provide an exciting opportunity to investigate the link between nuclear activity and galaxy formation5.
'The results presented at this conference have been obtained in collaboration with Andrea Comastri, Emanuele Daddi, Lucia Pozzetti, Gianni Zamorani, Andrea Cimatti, Cristian Vignali, Fabrizio Fiore, and Marco Mignoli.
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1.1. Fraction of A G N EROS
In this framework, we have started an extensive program of multiwavelength observations of the largest sample of EROs available to date', selected in a contiguous area (- 700 arcmin2) down to a magnitude limit of K s =19.2. We have obtained a total of -80 ks observation with XMM-Newton; the high-energy throughput of XMM-Newton, coupled with the large field of view, are well-suited to assess the fraction of AGN among a statistically significant sample of EROs at relatively bright X-ray fluxes6. Among the 312 EROs which fall within the XMM-Newton area ( w 380 arcmin2) analysed in Brusa et al. (2004), ten are individually detected in the X-rays. The fraction of X-ray detected (i.e. AGN-powered) EROs at Ks=19.2 and F 0 . 5 - 1 o k e ~ ;2 2 x erg cm-2 s-'is therefore 3%. Conversely, the fraction of EROs among hard X-ray sources is much higher (- 15%).
-
1.2. X - r a y to optical properties
In order t o investigate the nature of hard X-ray selected EROs and the link between faint hard X-ray sources and the ERO population, we have collected from the literature a sample of 111 X-ray detected EROs (including the 10 in our sample); for 52/111 photometric or spectroscopic redshifts are available (data from Lockman Hole3, CDFN7, CDFS', l i t e r a t ~ r e ~ > ~ l ~ ~ ) This sample is by no means homogeneous (e.g. the selection criteria for EROs are slightly different, R-K> 5 or I-K> 4 depending on the authors; or the K-coverage is not complete), but could be considered representative of EROs individually detected in the X-rays. The R-band magnitudes plotted versus the hard X-ray fluxes are reported in Fig. 1 (left panel): about half of the sources show an X-ray-to-optical flux ratio (X/O) larger than 10, shifted up by one order of magnitude from that of BL AGN, confirming independent results from near infrared observations of X-ray sources selected on the basis of their high X/O1'. 2. X-ray Properties of AGN EROs
First results suggested that the AGN population among EROs, although not dominant, shares the same X-ray properties of high luminosity, highly obscured AGN, the so-called quasar 2 (QS02)3>12713. In order to check whether X-ray absorption is common among these objects, we have quantitatively estimated the intrinsic X-ray column densities for
a3 E '
"
"
"
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"
"
"
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52 EROI with z (spec or phot)
From: CDFS 20
42
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43 0.5-10
44
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Figure 1. (left panel) R-band magnitude vs. hard X-ray flux for EROs, serendipitously detected in hard X-ray surveys. (Triangles = EROs in the "Daddi Field"; Open circles = EROs in the reference sample; filled circles = EROs with redshifts - see text for details). Broad Line AGN detected in the CDFS and CDFN surveys are also reported (small squares). The shaded area represents the region occupied by known AGN (e.g. quasars, Seyferts, emission line galaxies) along the correlation log(X/O) = 0 f 1. (right panel) Logarithm of the unabsorbed, full band X-ray luminosity versus the logarithm of the absorbing column density (NH) for all the X-ray detected EROs with spectroscopic or photometric redshifts from the comparison sample (open circles). Filled symbols are EROs with X/O > 10 (see text). The boxy region indicates the locus of Q S 0 2 .
the 52 EROs with a reliable spectroscopic or photometric identification. Column densities for the sources detected in the CDFN and CDFS have been obtained by fitting the observed counts with a single power law model plus absorption in the source rest-frame. For the sources in the Lockman Hole and in the "Literature" sample, the best-fit values quoted by the authors have been adopted. In all the cases, X-ray luminosities were estimated from the observed X-ray fluxes and corrected for absorption. The results are reported in the right panel of Fig. 1. Almost all of the individually detected EROs have intrinsic NH > crnp2, and they actually are heavily obscured AGN. This study confirms previous evidences mainly based on a Hardness Ratio analysis12 and on few isolated e x a m p l e ~ ~ yand ~ 1 ~unambiguously ~, indicates that large columns of cold gas (even > cm-2) are the rule rather than the exception among X-ray bright EROs. 3. EROs and QS02: a selection criterion
Given the high-redshift of these objects ( z k 1) and the average X-ray flux of the comparison sample (- 4 x erg cm-2 s-l ), it is not surpris-
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ing that the majority of X-ray detected EROs have high X-ray luminosities (Lx > erg s-l). Moreover, according to our analysis, a significant fraction of them have X-ray luminosities exceeding erg s-l, and therefore lie within the quasar regime. The large intrinsic column densities further imply that AGN EROs, selected at the brightest X-ray fluxes, have properties similar to those of QS02, the high-luminosity, high-redshift Type 2 AGNs predicted by X-Ray Background synthesis model^^^^^^. Among the X-ray detected EROs, the higher is the luminosity, the higher is the X-ray to optical flux ratio (filled symbols in right panel of Fig. 1). This confirms that a selection based on X/O > 10 is a powerful tool to detect high-luminosity, highly obscured sources, and it is even stronger when coupled with a previous selection on the extremely red colors. Given that the search for Q S 0 2 on the basis of detection of narrow optical emission lines is very difficult and is already challenging the capabilities of the largest optical telescopes, the proposed “alternative” method which combines near-infrared and X-ray observations, could provide a powerful tool to uncover luminous, obscured quasars.
Acknowledgments
I kindly acknowledge support by INAOE, Mexico, during the 2003 Guillermo-Haro Workshop where part of this work was performed.
References 1. E. Daddi et al., A & A 361, 535 (2000). 2. I. Lehmann et al., in X-rays at Sharp Focus Chandra Science Symposium, (2001). (astro-ph/0109172) 3. V. Mainieri et al., A & A 393, 425 (2002). 4. C. Willott et al., M N R A S 339, 397 (2003). 5. G.L. Granato et al., M N R A S 324, 757 (2001). 6. M. Brusa et al., A & A submitted, (2004). 7. A.J. Barger et al., A J 126, 632 (2003). 8. G.P. Szokoly et al., ApJS submitted (2004). (astro-ph/0312324) 9. C.S. Crawford et al., M N R A S 324, 427 (2001). 10. M. Brusa et al., A & A 409, 65 (2003). 11. M. Mignoli et al., A & A in press (2004). (astreph/0401298) 12. D.M. Alexander et al., A J 123, 1149 (2002). 13. P. Severgnini et al., in Multiwavelength Mapping of Galaxy Formation and Evolution (2004). (astro-ph/0312098) 14. J.A. Stevens et al., M N R A S 342, 249 (2003). 15. A. Comastri et al., M N R A S 327, 781 (2001). 16. R. Gilli, M. Salvati & G. Hasinger, A & A 336, 407 (2001).
THE NATURE OF THE SOURCES OF THE MID-IR BACKGROUND LIGHT*
c. SANCHEZ-FERNANDEZ~ XMM-Newton SOC P.O. BOX 50727 28080 Madrid, Spain E-mail:
[email protected]. es
Deep mid-IR galaxy surveys performed with ISOCAM have revealed a population of dust-obscured sources, for which the observed source density is in large excess with respect to the Euclidean predictions, and which suffices to account for about 60% of the diffuse infrared background light (IBL) at 15 pm. Synthesis models for the hard X-ray background, which require a large population of heavily obscured AGNs, predict that a large fraction of the accretion power in the Universe is absorbed. The absorbed energy is expected t o be re-emitted in the IR-mm waveband. Key current questions are: What is the nature of the sources in the IR population, and what fraction of the deep X-ray and mid-IR populations are related.
1. Introduction The extragalactic infrared background contains the majority of the emitted star-formation energy in the universe integrated over cosmic time'. The nature of its dominant sources has therefore been the subject of intense study, analogous to, and almost in parallel with, the resolution of the Xray background, which has been shown to be dominated by AGN2. Against the ongoing efforts t o achieve the deepest possible surveys on the well established deep fields, and considering the emerging potential of gravitational lensing through clusters of galaxies to search for background objects t o a depth not otherwise achievable, a deep-survey programme a t 15 and 7 pm was carried out with ISOCAM through the massive gravitationally lensing clusters of galaxies Abell 2390, Abell 2218 and Abell 3703. Detailed models of the clusters have been used to correct for the effects of gravitational lensing on the background source population. *This work is supported by ESA t o n behalf of the ARCS consortium
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86 2. The benefits of observing through a gravitational lens Since the optical identification of the first gravitational lens4, observations of cluster lenses have been extended t o most other wavelengths. Magnification due to lensing brings into view sources otherwise too faint to be detected, achieving better sensitivities than ultra-deep blank field surveys. Simultaneously, lensing causes a surface dilation effect, reducing source confusing. The expansion of apparent surface area in passing from the source plane to the observed sky is very significant near the center of the lens, and commensurate flux amplification and reduction of source confusion a t a given flux follow. The weakest sources detected in our survey have lensing corrected fluxes of 5 and 18 p J y at 7 and 15pm, respectively.
3. Results - number counts and contribution to the Extragalactic Background Light 15pm and 7pm source counts were extracted for the three fields to 80% and 50% completeness levels, which approximate to 5 a and 4a minimum thresholds, respectively. Roughly -70% of the 15pm sources are field sources lensed by the clusters. Of the sources detected only a t 7pm, 95% are cluster galaxies. The field 15pm counts, corrected for the effects of completeness, contamination by cluster sources and lensing, confirm earlier results of an excess by a factor of order 10 over no-evolution models5. The lensing results make an important contribution to the faintest 30% of the resolved background light and contribute roughly the faintest 10% of the resolved fraction (see Figure 1). These mid-IR luminous galaxies have been interpreted as a population of dust-enshrouded star forming galaxies’. Within the current detection limits, they occur mostly a t redshifts between 0.4 and 1.5 with a median redshift of about 0.8 over all ISOCAM deep surveys. The 15 pm counts cannot be explained without invoking either a strong evolution of the whole luminosity function6i7 or preferentially a sub-population of starburst galaxies evolving both in luminosity and density7>’. For the counts at 7pm, integrating in the range 14 pJy t o 460 pJy, we resolve (0.49 f 0.2) x lo-’ W m-’ sr-l of the Cosmic Infrared Background light into discrete sources. At 15pm, and including the counts from other extensive ISOCAM surveys to integrate over the range 30 pJy to 50 mJy, we reach two to three times deeper than the unlensed surveys to resolve (2.7f0.62)~10-’ W m-’ sr-l. These values correspond to 10% and 55%,
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respectively, of the infrared background light derived from photon-photon pair production of the high energy gamma rays from BL-Lac sources on the infrared background photons (see Figure 2 ) .
L
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ARCS thB w r k [subsumes the A23#) data prevlousy used to derhre Rnslngmunts on AZ39Oalone(Atth?rlet at. 1999.1
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.
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1 mag deeper than the SDSS NGP sample. Two out of 32 objects classifiable as broad-line AGN were consistent with intrinsic reddening E(B-V) 5 0.4 mag. Even redder objects are present in the sample, but not yet confirmed. This pilot program was to refine selection technique and shows the way to efficient sample selection.
The scientific goals of our multi-color selection of a sample complete in K magnitude2 are to 1) compare the completeness of optical color outlier and K excess samples; 2) detect a complete sample of quasars in the “redshift desert” 2.5 < z < 3.2; 3) determine the population fraction of red quasars; and 4) ultimately measure the K-band luminosity function to z=4. Initial spectroscopic runs with WIYN/Hydra and WHT/WYF’FOS in March, 2003, were designed to test our color selection efficiency and give a preview of object types and redshift range. The selection criterion (I - K) > 1 (R - I) distinguishes reddened quasars from the stellar locus. One area of the NDWFS Bootes Field’ of 0.85 sq. deg. was investigated with four configurations of the WIYN / Hydra multi-fiber spectrograph and one with the WHT WYFFOS. Each Hydra configuration targeted 70 different objects, many very faint. Exposure time was 220 minutes/configuration. Classifiable spectra were obtained for (nearly) all objects with R 5 20.4 mag. Given our spectroscopic completeness, the color selection criterion, and the sample limit of K cm-2 should all be detected with Spitzer, in principle allowing for a complete study of the AGN population in this field and providing a test both for the unified model of AGN and population synthesis models used t o explain the X-ray background.
References 1. M. Giavalisco, et al, A p J 6 0 0 , L93 (2004). 2 . M. Nenkova, Z. Ivezic and M. Elitzur, ApJ 570, L9 (2002). 3. C. M. Urry and E. Treister, this volume.
THE PACYDEFICIT IN IRAS 20100-4156'
J. R. VALDES AND A. BRESSAN Instituto Nacional de Astrofisica, Optica y Electrdnica, Puebla, Pue., M6xic0, Osservatorio Astronomic0 d i Padova, Italy
S. BERTA, A. FRANCESCHINI AND G. RODIGHIERO Dipartimento d i Astronomia, Padova, Italy D. RIGOPOULOU Department of Physics (Astrophysics), University of Oxford, O X I 3RH, UK
IRAS 20100-4156, being one of the most luminous local Ultraluminous Infrared Galaxies (ULIRGs), is one of the best templates for the analysis of high redshift dust enshrouded galaxies. We present the results of a NIR medium resolution spectroscopic study of this object, carried out with SOFI at ESO 3.5m NTT. Our detection of the Pan line provides ideal constraints on the dust extinction, SFR and presence of an AGN.
1. The recombination photon deficit
NIR spectra at different position angles (P.A.=-24 and P.A.= 56) were taken to trace the complex morphology of IRAS 20100-4156. Our spectroscopic data were compared with optical spectroscopy by Duc et al.4 and IRAS FIR fluxes. The SFRs, derived from the Ha! and P a a emission lines, even corrected for the attenuation determined by NIR-Optical emission lines decrement ratios (A~-3mag), and for aperture losses,l is more than one order of magnitude less than expected from the FIR luminosity ( S F R ~ ~ = 6 0 M o y r -SFRp,,=58Moyr-l, ~, SFR~1~=934Moyr-l). This confirms, at least in this object, the NIR recombination photon deficit already found in the Bry line of other ULIRGS.~ It is difficult to explain a 90% P a a deficit entirely with an obscured AGN because, with S(1.425GHz)z 20.3 ~ J YIRAS , ~ 20100-4156 falls on top of *Based on observations collected at ESO, Chile, ESO No. 67.A-0593, 71.A-0707.
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the FIR-radio relation of starburst galaxies, while a significant contribution of the FIR from the AGN would considerably affect its location on the r e l a t i ~ n Furthermore .~ our spectroscopic observations indicate only a marginal broadening underlying the Pacr line ( 4, we find a large scatter and no clear correlation between the millimetre and optical brightness (Figure 1). Lower average values of -MB and SZSOfor the SDSS sample compared with the PSS sample [20]and the low detection rate of the fainter souces studied in [23] are suggestive of a somewhat faint correlation. Let us note that the optically very bright QSOs targeted in this study are very rare and make a negligible contribution to the mm background [201. Although it is believed that starbursts contribute in a major way to the mm-submm emission of AGN (at least for the radio quiet ones), there
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is nevertheless t h e possibility t h a t t h e emitting dust is powered by t h e AGN radiation rather t h a n by t h e starburst. T h e best way t o confirm t h a t starbursts contribute in a major way t o t h e mm/submm continuum radiation detected is t o directly detect from CO emission t h e molecular gas which feeds t h e starburst, as discussed by Carilli e t al. in these proceedings.
References 1. D.B. Sanders & I.F. Mirabel, ARA&A 34, 749 (1996). 2. M.S. Longair, in Millimetre and Submillimetre Astronomy, ed. R.D. Wolstencroft and W.B. Burton, ASSL, 147, 343 (1988). 3. A.W. Blain & M.S. Longair MNRAS 264, 509 (1993). 4. S.E. Scott et al., MNRAS331, 817 (2002). 5. A.W. Blain, I. Smail, R.J. Ivison, J.P. Kneib & D.T. Frayer, Phys. Reports 369, 111 (2002). 6. F. Bertoldi et al., A&A 360, 92 (2000). 7. S.C. Chapman, A.W. Blain, R.J. Ivison & I.R. Smail, Nutur 422, 695 (2003). 8. S.C. Chapman, A.W. Blain, R.J. Ivison & I.R. Smail, in preparation (2004). 9. A.W. Blain, S.C. Chapman, I.R. Smail & R.J. Ivison, ApJ in press (2004). 10. R. Genzel et al., ApJ498, 579 (1998). 11. R.G McMahon et al., MNRAS 267, L9 (1994). 12. A. Omont et al., A&A 315, 1 (1996). 13. K.G. Isaak et al., MNRAS 269, L28 (1994). 14. K.G. Isaak et al., MNRAS 329, 149 (2002). 15. R.S. Priddey et al., MNRAS 339, 1183 (2003). 16. E.N. Archibald et al., MNRAS 323, 417 (2001). 17. M.J. Page et al., Science 294, 2516 (2001). 18. E. Kreysa et al., SPIE 3357, 319 (1999). 19. A. Omont et al., A&A 374, 371 (2001). 20. A. Omont et al., A&A 398, 857 (2003). 21. C.L. Carilli et al., ApJ 555, 625 (2001a). 22. M.P. Vkron-Cetty & P. VBron, A&A 374, 92 (2001). 23. A. Beelen, A. Omont, F. Bertoldi, P. Cox & C.L Carilli, in preparation (2004). 24. X. Fan et al., AJ 125, 1649 (2003). 25. F. Bertoldi & P. Cox, A&A 884, L11 (2002). 26. F. Bertoldi, C.L. Carilli, P. Cox, X. Fan, M.A. Strauss, A. Beelen, A. Omont & R. Zylka, A&A 406, L55 (2003). 27. C.L. Carilli et al., AJ 122, 1679 (2001). 28. A.O. Petric et al., in preparation (2004). 29. D.J. Benford, P. Cox, A. Omont, T.G. Phillips & R.G. McMahon, ApJ 518, L65 (1999).
MOLECULAR GAS IN HIGH REDSHIFT QSOS
c. L. CARILLI~,F. BERTOLDI~,F. WALTER~,K.M. MEN TEN^, A. BEELEN3, P. COX3 AND A. OMONT4 'National Radio Astronomy Observatory: 2Maz-Planck Inst. for Radio Astronomy, Uniu. Paris-Sud, 41nst. d'Astrophysique d e Paris E-mail:
[email protected] We review cm and mm observations of thermal molecular line emission from high redshift QSOs. These observations reveal the massive gas reservoirs ( 1O1O to 10l1 M o ) required to fuel star formation at high rates. We discuss evidence for active star formation in QSO host galaxies, and we show that these high redshift, FIR-luminous QSOs follow the non-linear trend of increasing LFIR/L'(CO) with increasing LFIR. We conclude with a brief discussion of the recent CO detection of the most distant QSO at z = 6.42, and its implications for cosmic reionization.
1. Introduction Over the last few years, the study of high redshift QSOs has been revolutionized in three ways. First, wide field surveys have revealed 100's of high z QSOs, right back to the epoch of cosmic reionization ( z > 6; e.g., Fan et al. 2003). Second, it has been shown that most (all?) low redshift spheroidal galaxies have central super-massive black holes (SMBH), and that the black hole mass correlates with bulge velocity dispersion. This MBH-O" correlation suggests coeval formation of galaxies and SMBH, thereby making SMBHs a fundamental aspect of the galaxy formation process (Gebhardt et al. 2000). And third, mm surveys of high redshift QSOs find that 30% of the sources are 'hyper-luminous infrared galaxies' ( L F I R= 1013 La), corresponding to thermal emission from warm dust, and that this fraction is independent of redshift out to z = 6.4 (Omont et al. this vol.). If the dust is heated by star formation, the implied star formation rates are extreme (> lo3 M a year-'), consistent with the formation of a large elliptical galaxy on a dynamical timescale of 10' years. On the other hand, the FIR *the national radio astronomy observatory is a facility of the national science foundation operated under cooperative agreement by associated universities, inc.
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luminosity constitutes typically only 10% of the bolometric luminosity of the sources, such that dust heating by the AGN remains an alternative. Demographic studies show that SMBHs acquire most of their mass during major accretion events marked by the QSO phenomenon (Yu & Tremaine 2002). Molecular line observations (typically CO) of FIR-luminous high z QSOs have revealed large gas masses in most cases observed to date (see Table 1). Such gas reservoirs are a prerequisite for star formation models for dust heating in FIR-luminous high z QSOs. The typical gas depletion timescales are of order lo7 to 10' years, if the dust is heated by star formation. In this review we consider this question in more detail. We restrict ourselves to z > 2 QSOs (see also Barvainis 1999; and see Scoville et al. 2004 and Sanders & Mirabel 1996 for observations of lower redshift QSOs). We assume a standard concordance cosmology.
2. Statistics Table 1 shows all the published detections of CO emission from sources at z > 2 (only the most recent reference is given). Many of the sources are AGN (QSOs, radio galaxies = RG), since in these cases optical spectroscopic redshifts are available, although a number of optically brighter 'submm galaxies' (SMM) have now been detected in CO emission (Neri et al. 2003), plus an optically selected Lyman-break galaxy (LBG; Baker et al. 2004). About half the sources are strongly lensed (L). Most sources have been studied in the higher order transitions (2 CO 3-2), although at z 2 4 the lower order transitions become accessible to cm telescopes such as the VLA. Figure 1 shows the correlation between FIR luminosity and velocity integrated CO 1-0 luminosity (L&o(l-o) K km s-l pc') for sources a t low and high redshift (Beelen et al. 2004). The sources in Table 1 consitute most of the sources with L F ~ > R 1013 La in Figure 1. For sources without CO 1-0 measurements, the 1-0 luminosity was calculated assuming constant brightness temperature. For the high redshift sources the FIR luminosity is given approximately by: L F J R= 4 x 1012(S250/mJy)La, appropriate for a typical ULIRG SED (Omont et al. al. 2003; note that in Fig 1 the values were calculated using the measured multifrequency SEDs where available). For dust heating by star formation, the total star formation rate (SFR; from ~ ~year-'. Gas masses 0.1 to 100 M a ) is given by: S F R = 4 x 1 0 - l o L ~Ma can be derived from: M(H2) = X x L&o(l-o), where X = 4 for typical spiral
117 Table 1. CO sources at z name B1021+4724 51636+4057 53W002 50443+0210 Cloverleaf J1401+0252 J1409+5628 B0414-0534 cB58 51230+1627 50911+0551 50239-0136 J0413+1027 J2330+3927 B0751+2716 J0943+4700 J0121+1320 J1909+722 4660.07 B0827+5255 52322+1944 B1335-0417 B0952-0115 B1202-0725 51148+5251
type
QSOL SMM QSO SMM QSOL SMML QSO QSOL LBGL QSOL QSOL SMML QSOL RG QSOL SMM RG RG RG QSOL QSOL QSO QSOL QSO QSO
z 2.286 2.385 2.394 2.509 2.558 2.565 2.583 2.639 2.727 2.735 2.796 2.808 2.846 3.094 3.200 3.346 3.520 3.534 3.788 3.911 4.119 4.407 4.434 4.693 6.419
Trans. 3-2 3- 2 3-2 3-2 3-2 3-2 3- 2 3- 2 3- 2 3- 2 3-2 3-2 3-2 4-3 4-3 4-3 4- 3 4-3 1-0 1-0 2- 1 2- 1 5-4 2- 1 3- 2
> 2 as of February L’ Jy km/s 4.2 2.3 1.2 1.4 9.9 2.4 4.0 2.6 0.3 0.80 2.9 3.1 5.4 1.3 6.0 1.1 1.2 1.6 0.24 0.15 0.92 0.44 0.91 0.49 0.20
s250
mJy 9.6 2.5 1.7 1.1 18 10.7 40 1 2.7 11.0 4.0 12.0 6.7 2.3 4 4.5 17.0 9.6 5.6 2.8 12.6 5.0
2004 ref Solomon 1992 Neri 2003 Alloin 2000 Neri 2003 Weiss 2004 F’rayer 1999 Beelen 2004 Barvainis 1998 Baker 2004 Guilloteau 1999 Hainline 2004 Genzel 2003 Hainline 2004 de Breuck 2003 Barvainis 2002 Neri 2003 de Breuck 2003 Papadopoulos 2000 Greve 2004 Papadopoulos 2001 Carilli 2003 Cox 2002 Carilli 2002 Guilloteau 1999 Carilli 2002 Walter03 Bertoldi04
galaxies, and X = 0.8 for ULIRGs (Downes & Solomon 1998). Note that X = 0.2 is the minimum (i.e. optically thin) value, assuming solar C and 0 abundances, and warm gas (70 K). The straight lines correspond t o linear relations, with a ratio of L F I R / L &= ~ 40 (dash) or 300 (solid). The correlation is clearly nonlinear, and is better described by a power-law of the form: L F I Rc( L&01.7. This non-linearity has been interpreted as an increasing ‘star formation efficiency’ (= SFR/gas mass) with increasing SFR (Gao & Solomon 2003). An alternate hypothesis is that the AGN dominates dust heating a t the highest luminosities. But this latter hypothesis begs the question: why would there be any correlation a t all? Meaning that if two very different physical mechanisms are involved, one might expect a discontinuity in this relationship going from starbursts to AGN.
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Figure 1. The relationship between L F I R and L/co(l-o) (Beelen et al. 2004).
3. Examples
Figure 2 shows examples of the CO excitation for three z > 4 QSOs. The line strengths are consistent with constant brightness temperature (TB)up to CO 5-4. This is similar to what is seen for nuclear starburst regions, such as in M82, and implies dense (> lo4 ~ m - ~warm ) , (> 50 K) gas. The recent detection of HCN emission from the Cloverleaf quasar at z = 2.56 supports the idea of dense, warm (star forming?) molecular gas in these systems (Solomon et al. 2003). Also shown in Figure 2 are the radio to IR SEDs of these sources. Again, the SEDs are similar to those seen in typical star forming galaxies. VLBA imaging of the 1.4GHz continuum emission from J1409+5628 at z = 2.58 implies intrinsic brightness temperatures < lo5 K, consistent with the nonthermal emission expected from a star forming galaxy, but inconsistent with that expected from an AGN (Beelen et al. 2004). Figure 3 shows the optical and CO emission from the z = 4.12 QSO 2322+1944. The source is strongly gravitationally lensed, appearing as a double QSO in the optical with 1” separation (Djorgovski et al. in prep), and a complete ’Einstein ring’ in the CO 2-1 emission. A similar ring is seen
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B1335-0417 2~4.41- squares JIl48t5251 ~ 4 . 4 2- triangles
0 1
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Figure 2. Left: The CO ladder for three high z QSOs. Right: T h e radio t o IR SEDs. The solid line is the fit for M82.
Figure 3. T h e optical (left) and CO 2-1 (right) images of the gravitationally lensed QSO J2322+1944 at z = 4.12 (Carilli et al. 2003).
for the 1.4 GHz continuum emission (Carilli et al. 2003). These results can be modeled in the source plane as a starburst disk surrounding the QSO with a radius of about 2 kpc. J2322+1944 represents perhaps the best example of a coeval starburst+AGN at high redshift. We consider briefly the question of why only 30% of high z QSOs are FIR luminous? Unfortunately, sensitivity limits of current (sub)mm surveys
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cannot rule out a continuum of FIR luminosities extending below a few mJy, although deep radio surveys suggest that this may not be the case (Petric et al. 2004 in prep). If there really are two types of QSOs (FIRluminous and FIR-quiet), then the 30% fraction could represent a relative duty cycle for star formation vs. QSO activity. Alternatively, there may be two types of major accretion events for SMBHs: those that have associated star formation, and those that do not. 4. Cosmic Stromgren spheres
The epoch of reionization (EoR) represents a fundamental benchmark in cosmic structure formation, corresponding to ionization of the neutral IGM by the first luminous sources. The recent discovery of Lya absorption by the neutral IGM toward z > 6 QSOs (the Gunn-Peterson effect; Fan et al. 2003) implies that these sources are situated at the end of the EoR.
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Figure 4. CO 3-2 emission from the highest redshift &SO, 51148+5251 at z = 6.419 (Walter et al. 2003). The left frame shows the velocity integrated line emission at 1.5” resolution at 46.7 GHz. The right frame is an ’off’ channel, showing the lack of continuum emission. The contour levels are: -0.1,0.1,0.2,0.3,0.4,0.5 mJy/beam.
Bertoldi et al. (2003) show that the 30% fraction of FIR-luminous QSOs remains constant into the EoR, including the most distant QSO known, J1148+5251, at z = 6.42, which has an L F I R = 1.2 x 1013 La. CO emission has also been detected from 51148+5251 using the VLA and the PdBI (Figure 4; Walter et al. 2003; Bertoldi et al. 2003), with an implied molecular gas mass of 2 x lo1’ M a . The presence of a large mass of heavy elements and dust in a galaxy just 0.8 Gyrs from the big bang raises interesting issues for ISM enrichment, and suggests that active star
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formation started at z > 10 in the host galaxy of this &SO. Also required is a dust formation mechanism involving high mass stars and/or supernova remnants . A particularly interesting result for J1148+5251 is the difference between the host galaxy redshift of 6.42 (as determined from the CO line) and the on-set of the Gunn-Peterson absorption trough at z = 6.32. We note these CO observations are the only measurements relating to the host galaxy properties (e.g. the exact redshift), as opposed to the AGN properties. This redshift difference implies that the QSO must be surrounded by a ionized sphere of physical radius R=4.7 Mpc, presumably formed by the radiation from the QSO itself. Hence, in J1148+5251 we are witnessing the process of cosmic reionization. This is a 'time bounded' Stromgren sphere, and implies a lifetime for the recent QSO activity of tqso= lo'(R/4.5M~c)~f(HI)years, where f(H1) is the (volume averaged) IGM neutral fraction (Walter et al. 2003; Wyithe & Loeb 2003a). Wyithe & Loeb (2003b) have used this result, plus models of QSO formation, to argue (statistically) that the neutral fraction of the IGM must be substantial at z = 6.4: f(H1) > 0.1, otherwise the QSO lifetimes become unreasonably short. This neutral fraction is much larger than the best current lower limits set by the GP effect of f(H1) > 0.001, and argues for 'fast reionization' at z 6 (Gnedin 2000). The implication is that f(H1) changes from < l o p 4 at z = 5.7 to > 10-1 at z = 6.4, ie. the neutral fraction of the universe changes by three orders of magnitude over a timescale of only 0.1 Gyr. N
References 1. D. Alloin et al., A p J 5 2 8 , L81 (2000). 2. A. Baker et al., ApJ (2004). 3. R. Barvainis, in Highly Redshifted Radio Lines, (ASP: San F'rancisco), eds. Carilli et al. p. 39 (1999). 4. R. Barvainis et al., A p J 4 9 2 , L13 (1998). 5. R. Barvainis et al., A&A 385, 399 (2002). 6. A. Beelen et al., A&A submitted (2004). 7. A. Beelen et al., A&A in prep (2004). 8. F. Bertoldi et al., A&A 409, L47 (2003). 9. F. Bertoldi et al., A B A 406, L55 (2003). 10. C. Carilli et al., Science 3 0 0 , 773 (2003). 11. C. Carilli et al., A J 1 2 3 , 1838 (2002). 12. P. Cox et al., A&A 387, 406 (2002). 13. D. Downes & P. Solomon, ApJ 507, 615 (1998). 14. C. de Breuck et al., NewAR 4 7 , 285 (2003).
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15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36.
X. Fan et al., A J 125, 1649 (2003). D. Frayer et al., ApJ 514, L13 (1999). Y. Gao & P. Solomon, ApJ in press (2003). (astroph/0310339) K. Gebhardt et al., ApJ 539, L13 (2000). R. Genzel et al., ApJ 584, 633 (2003). N. Gnedin, ApJ 535, 530 (2000). T. Greve, R. Ivison & P. Papadopoulos, A&A in press (2004). S. Guilloteau et al., A&A 349, 363 (1999). L.J. Hainline et al., ApJ in press (2004). (astroph/0403194) R. Neri et al., ApJ 597, L113 (2003). A. Omont et al., A H A 398, 857 (2003). P. Papadopoulos et al., Nature 409, 58 (2001). P. Papadopoulos et al., ApJ 528, 626 (2000). D. Sanders & F. Mirabel, A R A & A 34, 749 (1996). N. Scoville et al., ApJ 585, L105 (2003). P. Solomon et al., Nature 426, 636 (2003). P. Solomon, D. Downes & S. Radford, Nature 356, 318 (1992). F. Walter et al., Nature 424, 406 (2003). A. Weiss et al., A&A 409, L41 (2003). S. Wyithe & A. Loeb, (2004a). (astro-ph/0401188) S. Wyithe & A. Loeb, (2004b). (astro-ph/0401554) Q. Yu & S. Tremaine, MNRAS 335, 965 (2002).
THE GTM/LMT PROJECT STATUS *
L. CARRASCO AND E. RECILLAS Instituto Nacional de Astrofisica, Optica y Electrdnica. Tonanttintla, Pue., MLxico E-mail:
[email protected],
[email protected] F.P. SCHLOERB F i v e College Radio Astronomy Observatory, University of Massachusetts, MA, U.S.A. E-mail:
[email protected] T he Instituto Nacional de Astrofisica, Optica y Electr6nica in M6xico and the University of Massachusetts in the USA are collaborating to build the world’s largest radio telescope t h at operates at short millimeter wavelengths. This facility, known as the Large Millimeter Telescope (LMT) or Gran Telescopio Milim6trico (GTM), is being erected at an altitude of 4600m on Volc6n Sierra Negra in the Mexican state of Puebla. Th e telescope will be a fully steerable dish with a diameter of 50m and an active surface which will be adjusted under computer control t o correct for thermal and gravitational deformations. Instruments include focal plane arrays t o image both continuum and spectral line emission from celestial sources. The LMT/GTM will be a n extremely powerful facility for studies encompassing almost every area of astronomy, including extragalactic and cosmological research. In particular, the high sensitivity, angular resolution, and mapping speed will enable detailed investigations of dusty objects such as AGNs and starburst merging galaxies out to very large redshifts.
1. The Site: Volcdn Sierra Negra
The LMT/GTM is a MBxico-USA bi-national project. It is building a 50 meter aperture antenna, the largest single aperture radio telescope of its kind. It shall go into commissioning phases at the end of 2005. The leading institutions are the INAOE (MBxico) and The University of Massachusetts
(USA). *This work is partially supported by CONACYT grant g28586-e
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The LMT is being built at an altitude of 4600 m atop Volc&nSierra Negra, an extinct volcanic peak in the state of Puebla, Mkxico. This location was selected following radiometric tests at a number of potential mountain top sites in M6xico. The 19 degree latitude was a significant factor in the site selection, and the LMT’s coverage of the southern sky will be very good, with the Galactic center culminating at an elevation of about 45 degrees. The atmospheric opacity at 225 GHz, is very low, with a median value corresponding to about 2 mm of precipitable water vapor during approximately 9 months of the year. During winter nights extremely low values of precipitable water vapor corresponding to submillimetric conditions are often encountered. For antenna performance, the most critical factor is the wind speed, since the wind load distorts the surface of the dish and also affects the antenna pointing. The median wind speed is 6 m/s, while the telescope has been designed with the goal of meeting its specifications a X = 3.0mm in a wind of 10 m/s.
2. The Telescope
The LMT will be an “open-air” telescope and its specifications of design are ambitious, i.e. an overall surface accuracy of 70 pm rms, with a pointing accuracy of 0.7” rms. The LMT characteristics lead to potential aperture efficiencies of 0.70 a t X = 3.0mm and 0.45 at X = 1.2mm with corresponding sensitivities of 2.2 Jy/K (2.0 Jy/K) at X = 3.0mm and 3.5 Jy/K (3.1 Jy/K) at X = 1.2mm. The FWHM beam size is 15” at X = 3.0mm and 6” at X = 1.2mm. Meeting these specifications requires an advanced antenna design. The adopted design employs various “active” systems to bring the final performance within the requirements. The easier of the two main challenges is the surface accuracy. A significant improvement over existing telescopes could be obtained with an open loop active surface which includes 180 moveable surface segments. Each segment consists of a surface panel of either carbon fiber or machined aluminium, supported by a stiff reaction structure attached t o the reflector backstructure with a subframe. In order t o correct for gravitational and thermal deformations, four actuators per panel will adjust the subframes in relation to the backstructure. Holographic technics will be used to check the surface setting at regular times. Under benign conditions, with no wind load and stable nighttime temperatures, the antenna designer predicts that the structure is capable of
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satisfying the basic pointing requirements. However, wind and thermal loads introduce significant pointing errors which must be sensed and compensated. The initial system will rely on standard techniques, such as the use of an antenna pointing model, thermal stabilization of the structure, and careful attention to the design of the antenna motion controllers. These basic principles will be supplemented by measurements to characterize the behavior of the structure, including inclinometers mounted near the telescope elevation axis and temperature sensors on the structure, which may be used with finite element models t o determine structural deformations and predict pointing errors. Ultimately, metrology systems to properly measure structural deformations, such as the shape of the primary and the location of the subreflector with respect to the best fit parabola, will be used to bring the pointing properties of the antenna toward the final performance goal.
3. Current Status The design of the LMT was made by MAN Technologie of Germany, the designer of the largest radio telescope currently operating a t these frequencies, the Institut de RadioAstronomie Millimktrique 30m dish in Spain. Construction of the LMT is well underway. The foundation and other concrete work a t the site is complete. The alidade has been completed and assembled at the site. The backstructure, which will support the surface panels, is being assembled a t the site. Most mechanical components have been fabricated and are being transported to the site. Some surface panels are being manufactured by Composite Optics, Inc., of San Diego, USA. The telescope is scheduled for commissioning in 2005. 4. Auxiliary Instruments
With nearly 2000 m2 of collecting area and an excellent surface accuracy, the GTM/LMT’s sensitivity will exceed that of existing millimeterwavelength telescopes. This basic sensitivity is enhanced for continuum observations by the single dish’s ability t o make use of very wide bandwidth incoherent detectors (bolometers), which can not be utilized by interferometers. The LMT will consequently take a valuable place in the world’s complement of millimeter-wave facilities. A binational GTM/LMT Science Team from UMass and INAOE has selected an initial set of instrumentation which emphasizes the special capabilities of the large single diss. Some of the instruments are ready, and
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others are under construction. Already completed and operating a t the UMass Five College Radio Astronomy Observatory (FCRAO) 14m telescope in Massachusetts is SEQUOIA; a 32-pixel focal plane array for the 85-115 GHz frequency band’, and its associated spectrometer. These instruments will be transferred t o the LMT when it begins operation. SEQUOlA is based on MMIC’s the lowest noise amplifiers ever built in this frequency range. After the LMT surface accuracy and pointing have consistently reached the goals described above, it is expected that the X = 1.3mm atmospheric window will be its fundamental frequency band. Initially, however, there will likely be an extended period of calibration, scientific observations at lower frequencies (A = 3mm). Development of a focal plane array for spectroscopy at 1 mm will take sometime and plans for it have been delayed. However, it is important to test the telescope for observations at these higher frequencies as soon as possible, both for scientific reasons and to evaluate telescope performance. To this purpose, a dual-polarization, sideband separation SIS (superconductor-insulator-superconductor) mixer receiver for the 210-275 GHz frequency band is being developed a t UMass as a precursor t o a focal plane array for this band. One of the strengths of a large single dish telescope is the ability to use wide band incoherent detectors to obtain very high continuum sensitivity. The LMT project is collaborating with the Bolocam group2, to obtain a sensitive bolometer array for the LMT. Bolocam I1 will be a second realization of the Bolocam I instrument, which has recently been used successfully at the Caltech Submillimeter Observatory. It provides 144 pixels and is designed to operate in the 2.1, 1.4, and 1.1 millimeter bands. Continuum maps at those wavelengths will provide us with a very high rate of detection of extragalactic cosmic sources, many of them dusty mergers and AGN’s a t very high redshifts. Whereas Bolocam I1 is optimized for mapping in one frequency band a t a time, a second continuum instrument known as SPEED is being designed for simultaneous multiband photometry. Measurements of the spectral energy distribution with SPEED will be able to determine both the thermal and the kinematical aspects of the Sunyaev-Zeldovich Effect.
5 . Conclusions
Several plans for scientific use of the GTM/LMT are, naturally, already being laid. Most of the scientific goals presented over 10 years ago t o the
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funding agencies: CONACyT in Mhxico and DARPA and NSF in the U.S. are still very valid. Many of these are in the area of cosmology and the early universe4, as well as in the study of star formation and molecular clouds in our Milky Way and other galaxies5. Astrobiological research perpectives and some important posibilities are discussed by Irvine et al. (2003).
Acknowledgments The GTM/LMT project is being supported by the Consejo Nacional de Ciencia y Tecnologia (Mhxico) and the U.S. Defense Advanced Research Projects Agency (DARPA contract MDA972-959C-0004). This work has been partially supported by CONACYT grant G28586-E.
References 1. N.R. Erickson, R.M. Grosslein, R.B. Erickson & S. Weinreb, IEEE Trans. Microwave Theory Tech. 47, 2212 (1999). 2. J. Glenn, J.J. Bock, G. Chattopadhyay, S.F. Edgington, A.E. Lange, J. Zmuidzinas, P.D. Mauskopf, B. Rownd, L. Yuen & P.A. Ade, SPZE Proc. 3357,326 (1998). 3. W.M. Irvine, A. Carramiiiana, L. Carrasco & F.P. Schloerb, 0r.Li.Ew.Bio.
33,597 (2003). 4. J.D. Lowenthal & and D.H. Hughes (eds.), Deep Millimeter Surveys: Zmplications for Galaxy Formation and Evolution, World Scientific, New Jersey, London, Singapore, Hong Kong, (2001). 5 . W.F. Wall, A. Carramiiiana & L. Carrasco (eds.), Millimeter- Wave Astronomy: Molecular Chemistry and Physics in Space, Kluwer-Academic Publishers, (1999).
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Miguel Chavez
La fiesta
WHAT POWERS HIGH-REDSHIFT SCUBA GALAXIES?
D. M. ALEXANDER Institute of Astronomy, Madingley Road, Cambridge, CB3 OHA, UK E-mail:
[email protected]. ac.uk We investigate the origin of the huge luminosities produced by high-redshift SCUBA galaxies using the combination of ultra-deep X-ray observations (the 2 Ms Chandra Deep Field-North) and deep optical spectroscopic data. Even though a large fraction of high-redshift SCUBA galaxies host AGN activity (upward of 38%), we argue that in almost all cases the AGNs are not bolometrically important (i.e. < 20%). Thus, most high-redshift SCUBA galaxies appear to be star-formation dominated.
1. Introduction
Blank-field SCUBA surveys have uncovered a large population of submillimeter (submm; X = 300-1000 pm) emitting galaxies (e.g. Smail et al. 1997; Barger et al. 1999; Blain et al. 1999). Due to a considerable amount of intensive multi-wavelength follow-up effort, it is becoming clear that almost all are dust-enshrouded galaxies at z > l (e.g. Ivison et al. 2000; Smail et al. 2002; Chapman et al. 2003). Central to the study of submm galaxies is the physical origin of their extreme luminosities (i.e. starburst or AGN activity). If these sources are shown to be ultra-luminous starburst galaxies then their derived star-formation rates suggest a huge increase in star-formation activity at z > 1. Conversely, if these sources are shown to be ultra-luminous AGNs then they will outnumber comparably luminous optical QSOs by x 1-2 orders of magnitude. Both of these scenarios provide challenges to models of galaxy formation and evolution. 2. AGN activity in SCUBA Galaxies The ultra-deep Chandra Deep Field-North (CDF-N; Alexander et al. 2003b) studies showed that a significant fraction of submm galaxies host AGN activity (Barger et al. 2001; Alexander et al. 2003a). Indeed, using the 2 Ms CDF-N survey, Alexander et al. (2003a, 2004), estimated that upwards of 38% of bright submm galaxies (f85oPm 2 5 mJy; S/N>4) harbor 129
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an AGN. The predominantly flat or inverted X-ray spectral slopes of these sources indicated that most are heavily obscured. Since a (possibly large) fraction of the intrinsic power of the AGN is being absorbed] an accurate calculation of the contribution it makes to the bolometric luminosity requires a good measurement of the amount of obscuration. The most critical determination of the amount of obscuration towards the AGN is whether or not it is Compton thick (e.g. Fabian et al. 2000). In Compton-thick AGNs (the most heavily obscured objects)] the observed X-ray emission may account for 6.5, and present broad-band SEDs of our most promising candidates.
1. Introduction
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The epoch of reionization has now been discovered as a protracted period reaching from z 20 4 6.5 However, prior to z 6.5 galaxy formation was already well underway (e.g. [3]). It is essentially impossible to study this 'grey age' at optical wavelengths, but great progress can be expected if radio and millimetre telescopes can be targeted on quasars observed within the reionization epoch. Radio-loud targets allow absorption studies that can probe the evolving neutral and molecular content of the high-z Universe 4 , and radio HI absorption is the only way of probing the neutral gas which goes on t o form stars. We could begin these studies with current facilities (e.g. the GBT and GMRT), and with the next generation of large radio telescopes, such as the LOFAR and the SKA, we will easily be able to reach depths of lower luminosity radio sources and still detect 21 cm absorption. Unfortunately, there are currently no known z > 6.5 radio-loud objects. This is because such objects are rare, l’. The sky-area and further information about the survey can be found in Jarvis et al.’. To summarize, there are approximately 10000 sources over an area of 1 quarter of the sky. N
3. Eliminating low-redshift radio sources
There is a challenging, but tractable, sifting problem to eliminate both galaxies and quasars at z < 6. This is done in four steps. (i) We have cross-correlated the radio sample with publicly available all-sky optical and near-IR imaging, i.e. SDSS, POSS and 2MASS, along with more general searches of known objects via the literature and NED. From this investigation we have optical IDS for about 67% of the objects in the northern sample (comprising quasars, low-redshift galaxies, BL Lac objects etc.). The remaining objects have no detectable optical emission, typically to R 21.5. (ii) We have initiated deeper targeted observations in R-band of the remaining sources in the northern hemisphere, with IGI at the 2.7 m at McDonald Observatory. Observations down to R 23 - 23.5 (depending on conditions) have shown that we again cut the source list down by approximately 65 per cent. These sources, generally extended objects which are presumably z 5 2 radio galaxies, are obviously not at z > 6.5, because like the z 6.5 quasars already known12, these must have zero flux below the redshifted Lyman limit due to the Gunn-Peterson trough. (iii) We use good-seeing near-IR imaging to find all the remaining quasars, and eliminate all the remaining galaxies. This part of the survey has been underway since August 2003 for the northern hemisphere, with a large allocation of time on the United Kingdom Infrared Telescope N
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135 (UKIRT). This is now 75 per cent complete with the other 25 per cent set t o be completed by August 2004. (iv) We take Z-band or near-IR spectra and find the z > 6.5 quasars. UKIRT-UIST has recently showed its capability in detecting quasar broademission lines in the highest redshift quasar known to date13 allowing an estimate of the black-hole mass in this quasar via the broad MgII emission line. Lyman-a is more than twice as bright as MgII in the composite SDSS quasar spectrum and the huge drop blueward of Lyman-a due to absorption by neutral hydrogen is also a very strong signature. Therefore, identification would be relatively easy in 20 min exposures on the Hobby-Eberly telescope with its planned J-band extension to its low-resolution spectrograph. We have also been granted time on the Gemini-North telescope to do Z-band spectroscopy of our highest priority candidates. The southern survey will commence in April 2004 using the ESO telescopes in Chile. N
4. z
> 6 radio-loud quasar candidates
It is already clear that our best candidates come in two flavours (Fig 1.). Flavour-1 are ‘textbook candidates’ (top panel) with smooth JHK spectral energy distributions (SEDs): although photometry gives only a crude estimate, it seems very likely that these are quasars at redshiks of a t least 6 (to explain the sharp break between I and J). Flavour-2 are ‘bumpy-SED’ objects (bottom panel) for which the only explanation we can find is that they are lightly-reddened quasars a t z 2.5. As the errors show, we cannot, however, rule out the possibility that these too are at z > 6, perhaps with some reddening, so each of these must be followed up spectroscopically too. To date we have six good z > 6 quasar candidates, follow-up spectroscopy of these in the near future will provide the information on their true nature, and hopefully provide us with the discovery of the first z > 6 radio-loud quasars. Discovery of such objects will lead to the first 21 cm absorption observations within the epoch of reionization with the new generation of radio telescopes operating at frequencies of v < 300 MHz, e.g. the LOFAR. N
References 1. A. Kogut et al., A p J S 148, 161 (2003). 2. R.L. Becker et al., AJ 122, 2850 (2001).
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Figure 1. SEDs for two of our best candidates, t h e dashed line is the SDSS composite quasar spectrum. (top) The quasar composite is redshifted to z = 6.7, and the solid horizontal lines are our photometric data points from our UKIRT observations. This is the 'textbook' SED of a z > 6.5 quasar. (bottom) A reddened (A, = 1) quasar composite redshifted to z = 2.5. This is our typical flavour-2 candidate. 3. R. Pello, D. Schaerer, J. Richard, J.-F. Le Borgne & J.-P. Kneib, A&A 416, L35 (2004). 4. C.L. Carilli, N.Y. Gnedin & F. Owen, ApJ 577,22 (2002). 5. P.A. Shaver e t al., Nature 384,439 (1998). 6. J.S. Dunlop & J.A. Peacock, MNRAS 247,19 (1990). 7. M.J. Jarvis & S. Rawlings, MNRAS 319,121 (2000). 8. M.J. Jarvis et al., MNRAS 327,907 (2001). 9. M.J. Jarvis et al., in AGN Physics with the Sloan Digital Sky Survey, ed. G. T. Richards and P. B. Hall (San Francisco: ASP) (2004). (astro-ph/0309379) 10. R.B. Rengelink et al., A&AS 124,259 (1997). 11. C. De Breuck et al., A&A 394,59 (2002). 12. X. Fan et al., A J 125,1649 (2003). 13. C.J. Willott, R.J. McLure & M.J. Jarvis, ApJ 587,L15 (2003).
TESTING THE HOMOGENEITY OF BRIGHT RADIO SOURCES AT 15 GHz
T. G. ARSHAKIAN~,E. ROS AND J. A. ZENSUS Max-Planck-Institut fur Radioastronomie, Auf d e m Hugel 69, 53121 Bonn, Germany E-mail:
[email protected] M. L. LISTER Department of Physics, Purdue University, 525 Northwestern Aue., W. Lufuyette, IN yrgor-2036, USA E-mail:
[email protected]. edu
A sample of radio-loud active galactic nuclei (AGN) at 2cm is studied to test the isotropic distribution of radio sources in the sky and their uniform distribution in space. The sample is complete at flux-density limits of 1.5Jy for positive declinations and 2Jy for declinations between '0 < 6 < -20'. The active galactic nuclei sample comprises 133 members. Application of the two-dimensional Kolmogorov-Smirnov test shows that there is no significant deviation from the isotropic distribution in the sky, while the generalised V/Vm test shows that the space distribution of AGN is not uniform at high confidence level (99.9%). This is indicative of a strong positive evolution of AGN with cosmic epoch implying that AGN (or jet activity phenomena) were more numerous at high redshifts. It is shown that the evolution depends strongly on luminosity: low-luminosity QSOs show a strong positive evolution, while high-luminosity counterparts do not seem to show any evolution with cosmic epoch.
1. The sample and results of statistical analysis
We investigate the homogeneity of the flux-density limited sample of the 2 cm VLBA" survey on the sky and in the space. The sample is compiled by Lister et al. (in preparation; see [1,2]) where the main selection criterion is *On leave from Byurakan Astrophysical Observatory, Byurakan 378433, Armenia tTGA is grateful to the Alexander von Humboldt Foundation for the award of a Humboldt Post-Doctoral Fellowship. aVery Long Baseline Array
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138 the flux-density limit a t 15 GHz; all variable sources with galactic latitude Ibl > 2.5" and with measured VLBA flux densities exceeding 1.5 Jy (2 Jy for southern sources) at any epoch since 1994 are included in the sample. The complete sample comprises 133 radio sources, all are active galactic nuclei: radio-loud and core-dominated. Most of them have superluminal radio jets on parsec-scales. There are 95 quasars, 21 BL Lacs, 9 radio galaxies, and 8 sources with no optical counterpartsb. We performed a two-dimensional Kolmogorov-Smirnov test to show that the sample is distributed uniformly on the sky. The generalised version of V/Vm test [3,4] is used t o show that the (V/Vm) = 0.589 f 0.027 which is indicative of a strong positive cosmological evolution of AGN with redshift. The BL Lacs show a similar trend, but this is not statistically significant because of the small number of sources. The distribution seems to be uniform for galaxies, i.e. with no luminosity evolution so far. The plausible explanation is that all 7 radio galaxies occupy the low redshift region where the density/luminosity evolution is negligible, but better statistics would be needed t o confirm this result. To investigate the dependence of radio luminosity on the generalised V/Vm statistic, we divided the sample of quasars in two equal subsamples above and below the absolute luminosity at 15 GHz, P15 = W Hz-l. For 46 low-luminosity quasars we find that (V/Vm) = 0.658f0.036 with the confidence level of 99.96%, indicative that the distribution of V/Vm is biased towards large values, while for 49 strong sources ((V/Vm) = 0.53 f 0.04, P = 41%) no significant deviation from a uniform distribution is found. The K-S test shows that these distributions are different a t 96% confidence level. The Student t test shows that the mean of V/Vm values for low- and highluminosity quasars are different a t high significance level, 0.011 (98.88%). The low-/high-luminosity quasars evolve differently with redshift which is indicative that the cosmic evolution depends strongly on luminosity.
References 1. K.I. Kellermann, R.C. Vermuelen, J.A. Zensus & M.H. Cohen, AJ 115, 1295 (1998). 2. J.A. Zensus et al., AJ 124,662 (2002). 3. M. Schmidt, A p J 151, 393 (1969). 4. Y . Avni & J.N. Bahcall, ApJ235,694 (1980).
bSee http://www,physics.purdue.edu/astro/MOJAVE/
for more details.
UNDERSTANDING THE RELATIONSHIP BETWEEN THE ENVIRONMENT OF THE BLACK HOLE AND THE RADIO JET: OPTICAL SPECTROSCOPY OF COMPACT AGN
T. G. ARSHAKIAN*, E. ROS AND J. A. ZENSUS MPIfR, Bonn, Germany E-mail: tigar@mpifr-bonn. mpg. de
V. H. CHAVUSHYAN INAOE, Puebla, Mkxico E-mail:
[email protected] We aim to investigate the relationship between radio jet activity on parsec-scales and the characteristics of both the bright active galactic nuclei (AGN) and their broad line regions (BLR). For this purpose, we combine 2cm VLBAa observations of AGN with their optical spectral observations. This would enable us to investigate the optical spectra of a set of 172 relativistically beamed, flat-spectrum AGN with the nuclear disk oriented near the plane of sky. Here we present first results from optical spectroscopic observations of the brightest AGN from the 2 cm VLBA survey, and discuss the diversity of their spectral morphologies.
The sample and motivations. We intend to combine high-frequency observations of AGN with their optical spectral observations t o study interconnections between the parsec-scale radio jet properties, central black holes and their optical environments. For this purpose, we use the sample of compact radio sources observed at 15 GHz (2 cm) with the VLBA". Over 170 sources have been observed since 1994 (see [1,2] for selection criteria and other details). All AGN are radio loud and core-dominated. Most of them possess one-sided jets and superluminal motions on parsec scales. This can be explained if the jet/counterjet are intrinsically symmetric and *On leave from Byurakan Astrophysical Observatory, Byurakan 378433, Armenia tTGA is grateful to the Alexander von Humboldt Foundation for the award of a Humboldt Post-Doctoral Fellowship. This work partially supported from the CONACyT research grant 39560-F (MBxico). aVery Long Baseline Array
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relativistic: the relativistic Doppler boosting favors the source detection, appearing those as one-sided jet [3,4],and the small angle between the jet direction and the line of sight leads to superluminal motions. Most of the jet viewing angles are small, with a maximum viewing angle of 30" for quasars and BL Lacs [5]. It implies that most of the relativistically beamed, flat-spectrum AGN have nuclear disks seen nearly face-on. Therefore, the combination of 2 cm VLBA observations and optical spectroscopic observations is important for investigating the spectral properties of AGN, which are not biased by their orientation. Our main interests are: (i) to carry out an homogeneous detailed spectral classification of AGN and relate it to their radio spectral/morphology classification, (ii) to investigate whether the properties of the VLBA jets relate to the black hole masses, and (iii) to investigate how the jet intrinsic properties relate to the geometry/kinematics of BLRs. N
Spectral observations. We carried out an homogeneous spectral classification of N 70 AGN from the 2 cm survey, using an intermediate resolution spectroscopy of optically bright (m < 17.5) AGN on 2m class GHAO (Cananea, Sonora) and OAN SPM (Baja California) telescopes. The wavelength coverage -3800A- 8000A, and spectral resolution 12-15A allowed us to detect a wide range of emission lines going from Hp to CIV depending on the redshift of the source. Spectral classification showed diversity of AGN morphologies: LINE%, Seyfert galaxies, BL Lacs, quasars and radio galaxies. Based on the NASA Extragalactic Database (NED), within this sample most of the objects have not a unique and unambiguous classification. Note that even using a bright sample of AGN it is common to find a significative percentage of objects which have been spectroscopically misidentified [6]. For example, the NED gives different spectral classifications for 0055+300 (elliptical galaxy, LINER, Sy3b, and Syl), while according to our classification it is a red elliptical galaxy. The detailed results will be published elsewhere. References 1. 2. 3. 4. 5. 6.
K.I. Kellermann et id., AJ 115, 1295 (1998). J.A. Zensus et al., AJ 124, 662 (2002). R.D. Blandford & M. Rees, MNRAS 1 6 9 , 395 (1974). T.G. Arshakian & M.S. Longair, MNRAS 311, 846 (1999). M.L. Lister & A.P. Marscher, A p J 4 7 6 , 572 (1997). M.-P. VBron-Cetty, P. VBron & A.C. Goncalves, A&A 3 7 2 , 730, (2001).
THE 6C** SAMPLE AND THE HIGHEST REDSHIFT RADIO GALAXIES
M. J. CRUZ, M. J. JARVIS, K. M. BLUNDELL AND S. RAWLINGS Oxford University Astrophysics, Denys Wilkinson Building, Keble Road, Oxford, OX1 3RH, United Kingdom We present a new radio sample, 6C** designed t o find radio galaxies at z discuss some of its near-infrared imaging follow-up results.
> 4 and
Why search for the highest redshift radio galaxies? Radio galaxies trace the most massive galaxies' (> 2L,) and are associated with the most massive black holes' ( M 109Ma) in the universe at every epoch. Recent studies support the idea that at 2 < z < 4 they reside in proto-clusters and are progenitors of the central brightest cluster galaxies3. The highest redshift radio galaxies ( z > 4) are therefore key targets for studies of formation and evolution of massive structures in the early universe. They are particularly useful in this respect as they are selected on the basis of their radio emission and thus free of problems associated with optical selection methods such as dust obscuration. Also, they tend not to have their optical and infrared emission dominated by non-stellar nuclear emission as is the case for quasars. The 6C** Filtered Sample This is a new sample of radio galaxies drawn from the 151MHz, 6C survey which has been filtered with radio criteria chosen to optimize the chances of finding radio galaxies at z > 4. It has been selected to be brighter than 0.5 Jy at 151MHz on an area of sky of 0.33sr and to exclude sources whose radio spectral index between 151 MHz and 1.4GHz are flatter than 1 or whose radio angular size are larger than 1 2 arcsec. These are characteristics invariably seen in very distant radio galaxies4s5y6. The selection criteria resulted in the 6C** sample comprising 69 objects; their location within the survey region is shown in Fig. 1 (left). Based on the work of Ref. 7 we expect to have at least two sources at z > 5 among them. 141
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Figure 1. Left: Location of all 6C** sources within the survey region. Right: The 1.4GHz radio contours overlaid onto a NIRI (Gemini) K-band image of a candidate z > 5 , 6C** radio galaxy. The image has a size of 14” x 18”.
Results and Discussion Deep K-band imaging follow-up with UFTI on UKIRT and NIRI on Gemini has provided us with near-infrared identifications for every member in our sample. K-band photometry provides an accurate method of redshift estimation by using the tightness of the K - z diagram’. We estimate that 40 % of the sources on 6C** have redshifts > 2, in accordance with extrapolations from previous studiesg. By selecting the faintest ( K N 21) members on our sample we have identified five strong candidate z > 5 radio galaxies. One of them was not securely detected despite a 45 min. integration with NIRI, although there are hints of an object with K 22 close t o the limit of the observation (Fig. 1, right). Future spectroscopic observations will tell us about the nature of these sources and will secure their redshifts. N
N
Acknowledgments MJC acknowledges the support from the Portuguese FundaGiio para a Ci6ncia e e Tecnologia, and Corpus Christi College, Oxford. References M.J. Jarvis et al., M N R A S 326,1585 (2001). C.J. Willott, R.J. McLure & M.J. Jarvis, ApJ 587,L15 (2003). J. Kurk et al., astro-ph/U909675. P.J. McCarthy, A R A A 31,639 (1993). S. Rawlings et al., Nature 383,502 (1996). W.J. van Breugel et al., ApJ 518,L61 (1999). M.J. Jarvis et al., M N R A S 327,907 (2001). 8. C.J. Willott et al., M N R A S 339,173 (2003) 9. M.J. Jarvis et al., M N R A S 326,1563 (2001).
1. 2. 3. 4. 5. 6. 7.
THE FIRST FLAT SPECTRUM SAMPLE
G. FOSSATI* R i c e University, Houston, T X - gfossatiQrice. edu
The FIRST Flat Spectrum Sample (FFSS) is a deep radio-selected sample, unbiased with respect to X-ray emission. It is designed to enable us to determine the true census of the different types of blazars, resolving a long-standing uncertainty, and the first step towards understanding how Nature makes jets.
Blazars show a rich phenomenology spanning a very broad range of luminosities, SED “colors”, emission line properties, cosmological evolution, implying a large range of underlying jet properties. Contrary to earlier interpretations, in all cases the distinctions seem to be one of degree rather than a bimodality. Moreover, there is a strong hint that the “true dimensionality” of blazars parameter space is reduced to just one or two key physical properties. The new unification paradigm for blazars3 suggests that SED colors reveal the intrinsic power of the black hole/jet system. Finding out the proportion and the degree of continuity of SED colors, and the relationship between “color” and power are clearly necessary first steps towards understanding how Nature makes jets. Unfortunately, the demographics of blazar jets is very poorly known. Because of the range of blazar SEDs, shallow radio or X-ray surveys sample only the tip of the population, and only in selected “corners” of the parameter space. The interpretation of SED color distribution depends on the complicated sensitivity of diverse surveys to a range of spectral types. Larger, deeper, and carefully designed surveys in conjunction with new simulations will resolve the present uncertainty over the propensity for different blazar flavors4.
Making a “blazar samp2e ”- Observationally, the crucial points for improvements are: i) include in an unprejudiced way “red” and “blue” blazars. ii) Not distinguish a priori between BL Lac and FSRQ. iii) Be “weak-blazar” *The FFSS project is done in collaboration with S. Laurent-Muehleisen (UC Davis) and C.M. Urry (Yale). G F acknowledges partially support by grant SAO G03-4147X.
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aware, i.e. of the fact that sources with galaxy-like optical spectrum but blazar-like nuclear SED should probably be classified as BL Lac objects2. The FFSS is the only sample designed according to these guidelines. Selection: FFSS sources are selected solely on the basis of the flatness of their radio spectrum. We used the 6cm Green Bank catalog to identify sources with cxr 5 0.5. Unlike typical quasar searches, candidates were not excluded based on their optical color or morphology. We have ~ 5 5 0 candidates brighter than F2ocrn=35mJy and B=19.0 mag. Optical: identification is -90% complete, with optical spectra for 2200 new objects (Laurent-Muehleisenet al., in prep.). As expected, most objects are blazars. We have complete information on the optical properties including emission line equivalent widths and fluxes, and strength of the Ca break, which provides a sensible measure of the relative contribution of the nonthermal and thermal components5. It is worth noting that FIRST survey sky coverage coincides with that of the SDSS. The SDSS/DR2l includes 175 FFSS sources (92 with spectroscopy). An extrapolation of this match rate would yield SDSS photometry(spectra) for 400(250) FFSS objects. InfraRed: Correlation with the 2MASS All-Sky Point Source Catalog yields 328 matches (60%), 305 with detections in all three JHK bands. X-rau: The ROSAT All Sky Survey and the WGACAT yield 260 identifications (50%). We observed 13 objects with Chandra in Cycle4, and for 26 more there are Chandra archival data. The total number of X-ray observed sources is now 299 (39 with Chandra). The unique feature of the FFSS is that it is the first blazar sample. In its present status the FFSS comprises 2 9 0 BLLacs, -350 FSRQs, -70 “galaxies”. The mix is excellent also in terms of SED “color””: 25% of the objects are “blue” and 25% “red”. This sample is ideal for studying the transition between FSRQs and BL Lacs, and the sizeable galaxy subsample will allow investigation of the existence and properties of weak AGN. References K. Abazajian et al., A J , in press (2004). (DR2 comprises -40% of the surveys) I.W.A. Browne & M.J.M. MarchB, MNRAS 261,795 (1993). G. Fossati et al., MNRAS 299,433 (1998). G. Fossati, in Blazars Demographics and Physics, eds. P. Padovani, C.M. Urry (San Francisco: ASP), ASP Conf. Ser. 227,218 (2001). 5. H. Landt, P. Padovani & P. Giommi, MNRAS 336,945 (2002).
1. 2. 3. 4.
aA robust determination requires the X-ray flux, but in zero-th approximation we can use
QRO
as a proxy. Here we consider
( Y R O < _ ~for .~
“blue”, and c~~oLO.6 for “red”.
THE COSMOLOGICAL EVOLUTION OF THE ENVIRONMENTS OF POWERFUL RADIO GALAXIES
J.A.GOODLET AND C.R.KAISER School of Physics and Astronomy Southampton University SO17 1BJ United Kingdom E-mail:
[email protected] We present the results from the analysis of 26 extragalactic radio sources of type FRII which were observed with the VLA at 5 GHz and around the 1.4 GHz band. The sources were selected to have redshifts in the range 0.3 < t < 1.3, radio powers between 6.9X 1OZ6WHz-' < P 1 5 1 < ~ 1~ . ~ 3 1028WHz-1 ~ and angular size 0 2 10". We found that the depolarisation and the rms variations in the rotation measure increased with redshift. The flux values obtained from the observations were used t o derive by means of analytical modelling the jet-power, density of the central environment, age of the source and its lobe pressure and the results were then compared with the observations. We find no significant correlations with the density parameter suggesting that the depolarisation and the rms variations in the rotation measure are indicative of the environment becoming more disordered rather than denser. The age and size of a source are correlated and both were found to be independent of redshift and radio-power. Jet-power strongly correlated with the radio-power. The lobe pressure was found to be anti-correlated with size which could explain why there are no sources beyond a few Mpc in size. We found no significant correlation between size and density which demonstrates that the sample is a fair representation of the population.
1. Observations
To break the degeneracy effect found between radio-power and redshift in previous studies we defined 3 subsamples of sources chosen from the 3C and 6C/7C catalogues. For full details on the sample selection and the data reduction see Goodlet et d.',hereafter G04. Spectral index, rotation measure and depolarisation were derived from the observations and were averaged over individual lobes. We define the spectral index, a, by S, c( va. The difference in a, DM and RM between the two lobes of an individual source is given by d a , dDM and dRM respectively. The rms variation of the rotation measure is defined by U R M . 145
146
2. Theoretical modelling
The large scale structure of FRII sources is formed from twin jets emerging from a central AGN buried inside the nucleus of the host galaxy. The jets propagate in opposite directions from the core of the source and end in strong shocks. The jet material inflates a lobe surrounding the jet, which drives a bow shock into the surrounding medium. Kaiser & Alexander2 (KA) showed that in a purely dynamical model of FRII evolution, the bow shock and lobe grow self-similarly. The KA model assumes a powerlaw for the external density distribution, p = po (r/ao)-P and a constant rate of energy injection into the lobe, Q o . The length of the jet, Dlobe, grows with time proportional to t 3 / ( 5 - P ) Kaiser . et d 3 (KDA) added synchrotron radio emission to the dynamical model of KA. The model selfconsistently incorporates the effects of all relevant energy losses on the relativistic electrons giving rise to the synchrotron emission. This allows us t o calculate the total radio luminosity P, of the lobe. The density of P and is related to the Dlobe, Qo the environment is parameterised by aopo and the age of the source. Using the flux measurements a t our 3 observing frequencies and the model of KDA, we constrained the lobe pressure and external density of all sources in our samples. Qo and the source age were then calculated from the best fit parameters. 3. Results
DM and C T R M , which are indirect measurements of density, increase with redshift. Unfortunately this was not observed in the density parameter atp,. DM and O R M may increase with redshift because the environments are more disturbed rather than denser. This may fit with observations indicating a higher degree of distortions of the large scale radio structure of objects a t high redshift objects. Spectral index was found to be independent of all the other source properties. Larger sources are older, as expected for ram pressure confined jets. Sources with larger jet-powers are more luminous. Lobe pressure correlates strongly with lobe size and the radio luminosity of the source.
References 1. J.A. Goodlet, C.R. Kaiser, P.N. Best & J. Dennett-Thorpe, MNRAS 347, 508
(2004). 2. C. Kaiser & P. Alexander, MNRAS 286, 215 (1997). 3. C.R. Kaiser, J. Dennett-Thorpe & P. Alexander, MNRAS 292, 723 (1997).
CONSISTENCY BETWEEN THE RADIO & MIR SOURCE COUNTS USING THE RADIO-MIR CORRELATION
N. SEYMOUR Institut d'Astrophysique d e Paris, 98bis, Boulevard Arago, 75014 Paris, fiance
I. M ~ H A R D YAND K.F. GUNN School of Physics 6 3 Astronomy, University of Southampton, Highfield, Southampton, SO1 7 1B, UK We show from the recent extrapolation of the radio-FIR correlation to the MIR that the 20 cm and 15 pm differential source counts are likely to come from the same parent population.
The Radio-FIR correlation and source counts. The radio-FIR correlation is one of the tightest observational results in astronomy1 and has recently been extended to the MIR (directly2, and indirectly3). This relationship is interpreted as being due to different physical manifestations of star-formation a t different wavelengths. The differential number counts at 20 cm have long been known to have an up-turn below 1 mJy4, oft explained by the dominance of star-forming galaxies over AGNs (which dominate a t higher flux densities). The 20 cm counts have been modelled by Ref. 5 & Ref. 6 where luminosity-evolution of the local star-forming radio luminosity function must be evoked t o explain the shape of the curve. The 15 pm differential source counts also show a n up-turn below 1 mJy which exceed the counts from a non-evolving local luminosity function7. This excess a t 15 pm is also thought to be due to star-formation. Extrapolation to 20 cm of the 15 p m source counts. The fit of Ref. 7 to the 15 pm source counts can be superimposed upon the 20 cm source counts, to test for consistency, by applying the flux density ratio of objects which follow the radio-MIR correlation. To derive this ratio, 20 cm luminosities were K-corrected assuming a radio spectral index of a = -0.7 (5'0: v") and 15 pm luminosities were K-corrected using an M82-like spec147
148
trum (i.e. star-burst) for the LW3 ISOCAM bandpass8. The flux density ratio is found to be roughly constant (Fig. 1, left) as a function of redshift over the range used by Ref. 2 for the radio-MIR correlation, z < 0.7. By using a flux density ratio of 0.12 the contribution of star-forming galaxies observed at 15 pm is consistent with that at 20 cm (Fig. 1, right).
t
0
0.2
0.4
0.6
redshift 2
0.8
1.4 CH2 Flux (mJy)
Figure 1. Left: The 20 cm/15 pm observed flux density ratio derived from the radio/MIR correlation of Ref. 2 as a function of redshift (upper and lower limits from error in radio/MIR correlation). Right: The differential 20 cm source counts from the literature with the hatched region indicating the superposition of the 15 pm counts.
Conclusions and Comment. We have shown that the source counts at 20 cm and 15 pm below 1 mJy and the correlation of their rest frame luminosities are all consistent, suggesting that they are from the same parent population, possibly dominated by star-formation. We note though that this consistency depends strongly on the normalisation of the radio-MIR (cf the higher normalisation of Ref. 3) and also partly on the SED used for the 15 pm K-correction. Detailed analysis of the faint source population using Spitzer will shed light on the true relative contribution of star-formation and AGN within faint objects collectively and individually. References 1. C.L. Carilli & M.S. Yun, ApJ 530,618 (2000). 2. C. Gruppioni et al., MNRAS 341,L1 (2003). 3. M.A. Garrett, A&A 384,L19 (2002) 4. R. Windhorst et al., ASP Conf. Ser. 10, 389 (1990). 5. A.M. Hopkins, B. Mobasher, L. Cram & M. Rowan-Robinson MNRAS 296, 839 (1998). 6. N. Seymour, I.M. M'Hardy & K.F. Gunn MNRAS, submitted (2004). 7. D. Elbaz et al., A&A 351,L37 (1999). 8. A. F'ranceschini et al., A&A 378, 1 (2001).
Part 11. Results from Surveys
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Statistical Properties of Local AGN
152
Luis Ho and Raul Mujica
. .
Martin Haas and Henrique Schmitt
WHAT CAN W E LEARN FROM NEARBY AGNS?
L. C . HO The Observatories of the Carnegie Institution of Washington 813 Santa Barbara Street Pasadena, CA 91 101-1898, USA This contribution reviews the properties of nuclear activity in nearby galaxies, with emphasis on their implications for the demography of nuclear black holes and the nature of accretion flows in the regime of very low accretion rates.
1. Why Study Nearby AGNs? In a meeting largely devoted to surveys of distant, luminous AGNs, it is instructive to examine what we know about AGNs in very nearby galaxies. Nearby AGNs are important for several reasons. Since AGNs derive their power from accretion onto central black holes, the statistics of AGNs serve as a crude surrogate to delineate the demography of massive black holes in galaxies-a topic of considerable recent interest (see Ho 2004a)-which is otherwise accessible only through painstaking kinematical observations. With the growing realization that black holes, and thus AGN activity, are part and parcel of the life-cycle of many galaxies, there is growing urgency to bridge the substantial gap that now exists between our knowledge of the space density of luminous quasars and that of quasar remnants. The extant information on the luminosity function of AGNs fainter than, say, M B M -20 to -23 mag, is very sketchy at virtually any redshift, being practically nonexistent for M B -18 mag. A census of nearby AGNs can place a robust constraint on the very faint end of the local ( 2 M 0) AGN luminosity function. By virtue of their proximity, nearby AGNs also offer a special vantage point to probe with high linear resolution the properties of their host galaxies and local environment. This level of detail is indispensable, for example, if one wishes to understand the triggering or fueling mechanisms for AGNs. Finally, as the evolutionary endpoint of quasars, nearby AGNs present an opportunity to study black hole accretion in a unique regime of parameter space, namely when the accretion drops to exceedingly low
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Figure 1. Detection rate of AGNs as a function of Hubble type in the Palomar survey. T y p e 1” AGNs (those with broad H a ) are shown separately from the total population (types 1 and 2). (Adapted from Ho et al. 1997.)
rates. Much emphasis has been placed on how AGNs turn on; it is just as important to understand how they turn off. 2. Demography of Central Black Holes from AGN Surveys
To the extent that an AGN signature signifies accretion onto a massive black hole, a local AGN census gives us a lower limit on the fraction of nearby galaxies hosting massive black holes (see Ho 2004b). There are many ways to select AGNs. Most surveys rely on selection criteria that isolate some previously known characteristics of AGNs. A common strategy employs color cuts to highlight the blue continuum typically present in AGN spectra. Some use objective prism plates to identify objects with strong and/or broad emission lines. Other wavelength-specific techniques to find candidate AGNs include preselection by radio or X-ray emission, or by “warm” infrared colors. Variability is also occasionally used. While all of these techniques have been successful, each introduces its own biases, and all ultimately require follow-up optical spectroscopy to confirm the AGN identification, to classify its type, and to determine its redshift. Nearby AGNs are generally intrinsically faint. For these sources, most of the above-mentioned “tell-tale signs” are difficult or impossible to detect, either because they are severely diluted by the host galaxy or because they are intrinsically absent. To find local AGNs effectively, one has little recourse but to resort to brute force: direct spectroscopy of a magnitude-
155
limited sample of galaxies. The following discussion draws mainly from the Palomar spectroscopic study of nearby galaxies (Ho, Filippenko, & Sargent 1997, and references therein), which remains the most sensitive survey of its kind. The AGN samples emerging from the Sloan Digital Sky Survey (SDSS; Miller et al. 2003; Hao & Strauss 2004; Kauffmann et al. 2004) certainly eclipse the Palomar sample in size, and they provide much better statistics on sources with moderate and high luminosities, but they do not go as deep on the faint end of the luminosity function. Moreover, as emphasized by Ho (2004b), the relatively large physical scale sampled by the SDSS spectra complicates the interpretation of LINE%, locally the dominant constituent of the AGN population. Figure 1 gives an overview of the AGN detection rate in the Palomar survey. For conciseness, I do not distinguish the different subclasses of objects (Seyferts, LINE%, and transition objects), nor will I discuss the AGN “pedigree” of each; these topics have been recently reviewed elsewhere (Ho 2004b). The most pertinent points to draw from the figure are: 0
0
0
AGNs are very common in nearby galaxies. At least 40% of all galaxies (with BT 5 12.5 mag) emit AGN-like spectra. The detectability of AGNs depends strongly on the morphological type of the galaxy, being most common in early-type systems (E-Sbc). The detection rate of AGNs reaches 50%-75% in ellipticals, lenticulars, and bulge-dominated spirals but drops to 520% in galaxies classified as Sc or later. These AGN detection rates support the notion, popularized by dynamical studies, that central black holes are common in galaxies, and perhaps ubiquitous in those with bulges. This consistency check is important, and the apparent agreement should not be taken for granted, because direct dynamical detections of black holes are technically challenging and still limited by small number statistics.
3. Evidence for Intermediate-mass Black Holes The distribution of black hole masses based on direct dynamical measurements (see, e.g., Tremaine et al. 2002) currently does not extend below 3 x 10‘ M a , the mass of the central black hole in the Milky Way. The record holder may be NGC 4945 (-J 1 x 10‘ M a ; Greenhill, Moran, & Herrnstein 1997), but the kinematics of its nuclear H20 maser disk are not straightforward t o interpret. How far does the bottom end of the mass
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Figure 2. Two examples of AGNs in late-type galaxies. The left panel shows an optical image of NGC 4395, adapted from the Carnegie Atlas of Galaxies (Sandage & Bedke 1994); the image is -15’ (17 kpc) on a side. The right panel shows an R-band image of POX 52, adapted from Barth et al. (2004); the image is -25’’ (11 kpc) on a side.
function of black holes extend? Is there a sharp boundary between the masses of stellar and nuclear black holes? The current limit of 106 Ma most likely reflects our present observational sensitivity rather than a physical threshold. Intermediate-mass (- lo3 - lo5 M a ) black holes, if they exist, may offer important clues to the nature of the “seeds” of supermassive (lo6 - lo9 M a ) black holes. The inspiral of smaller black holes onto bigger ones, an inevitable consequence of hierarchical structure formation, may also provide a significant contribution to the integrated gravitational radiation background (e.g., Hughes 2002). To date, the only known cases of intermediate-mass black holes based on resolved kinematics come from studies of globular clusters (Gebhardt, Rich, & Ho 2002; Gerssen et al. 2002), which, in any case, have been controversial (Baumgardt et al. 2003a, b). Clearly, it would be desirable to establish whether intermediate-mass black holes exist in galactic nuclei. Nuclear intermediate-mass black holes would manifest themselves as AGNs of moderately low luminosities ( ~ 1 erg 0 s-’), ~ ~ most likely in low-mass or very late-type galaxies. Two such cases have recently been reported (Fig. 2). The nearby (- 4 Mpc), Magellanic spiral (Sdm) galaxy NGC 4395 has long been known to host a low-luminosity Seyfert 1 nucleus (Filippenko & Sargent 1989), which has been well studied from radio to X-ray wavelengths. Filippenko & Ho (2003) used several lines of evidence to argue that the mass of the central N
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Figure 3. The black hole mass vs. velocity dispersion relation extended to the regime of intermediatemass black holes. The dashed line shows the fit of Tremaine et al. (2002):
M.
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black hole in NGC 4395 lies in the range of lo4 - lo5 M a . This result is significant because it demonstrates unequivocally that nuclear black holes can exist in a bulgeless galaxy. Equally striking is POX 52, a considerably more distant (- 90 Mpc) dwarf galaxy. Barth et al. (2004) find that POX 52 has an optical spectrum that is virtually indistinguishable from that of NGC 4395. It also shows tentative evidence of X-ray emission. Based on the velocity width of the broad Balmer lines and the continuum luminosity, Barth et al. obtain a virial mass of lo5 M a . Interestingly, POX 52 appears to a dwarf elliptical galaxy, the first known to host an unambiguous AGN. This is quite unexpected because dwarf elliptical galaxies, while technically spheroidal
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systems, bear little physical resemblance to classical bulges. Dwarf ellipticals occupy a distinct locus on the fundamental plane of hot stellar systems (Bender, Burstein, & Faber 1992; Geha, Guhathakurta, & van der Mare1 2003), and they are thought to originate from harassment and tidal stripping of late-type (bulgeless) disk galaxies (e.g., Moore et al. 1996). Thus, like NGC 4395, POX 52 stands as testimony that a bulge is not a prerequisite for the formation of central black hole. Finally, another surprise (Fig. 3). Although no firm conclusions can yet be drawn based on such meager statistics, it is intriguing, indeed mildly perplexing, that the four new candidate intermediate-mass black holes (the globular clusters M15 and G1 and the AGNs in NGC 4395 and POX 52) evidently seem to obey the relation between black hole mass and stellar velocity dispersion established by supermassive black holes (Gebhardt et al. 2000; Ferrarese & Merritt 2000; Tremaine et al. 2002). Are AGNs in dwarf or late-type galaxies common? Evidently not, at least in the nearby Universe. NGC 4395 is one of a kind in the Palomar survey of -500 galaxies. On the other hand, POX 52 was discovered in an objective prism survey of a relatively small area of sky (Kunth, Sargent, & Bothun 1987), so objects like it cannot be that rare. Using the first data release from the SDSS, Greene & Ho (2004) have identified -150 AGNs that have sub-106 M o black holes. The SDSS images do not furnish reliable information on the host galaxy morphologies, but a sizable fraction of them appear to be relatively disk-dominated spirals.
4. The Optical Luminosity Function of
z
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0 AGNs
Many astrophysical applications of AGN demographics benefit from knowing the AGN luminosity function, @ ( Lz, ) . Whereas @ ( Lz, ) has been reasonably well charted for high L and high z using quasars, it is very poorly known at low L and low z . Indeed, until very recently there has been no re, Since nearby AGNs are faint, disentangling liable determination of @ ( L0). the nuclear emission from the much brighter contribution of the host galaxy poses a major challenge. It is unacceptable to simply use the integrated emission from the entire galaxy. Moreover, most optical luminosity functions of bright, more distant AGNs are specified in terms of the nonstellar optical continuum (usually in the B band) , whereas spectroscopic surveys of nearby galaxies generally only reliably measure optical line emission (e.g., Ha) because the featureless nuclear continuum is often impossible to detect in ground-based, seeing-limited apertures.
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Figure 4. The B-band nuclear luminosity function of nearby AGNs derived from the Palomar survey. The filled circles include all (type 1 type 2) sources, while the open circles include only type 1 sources. The sample of luminous Seyfert 1s and quasars from the Hamburg/ESO survey of Kohler et al. (1997) is shown as stars. A double power-law fit to the Palomar and Hamburg/ESO samples is shown as a solid (type 1 type 2) and dashed (type 1) curve. (Adapted from Ho 2004b.)
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The strategy adopted for the Palomar survey utilizes the well-known correlation between Balmer emission-line luminosity and optical featureless continuum luminosity, which has been shown by Ho & Peng (2001) to hold for low-luminosity AGNs. Figure 4 shows the B-band nuclear luminosity function for the Palomar AGNs. Two versions are presented, each representing an extreme view of what kind of sources should be regarded as bona f i d e AGNs. The open circles include only type 1 nuclei, sources in which broad H a emission was detected and hence whose AGN status is incontrovertible. This may be regarded as the most conservative assumption and a lower bound, since genuine narrow-lined AGNs do exist. The solid circles lump together all sources classified as LINE%, transition objects, or Seyferts, both type 1 and type 2. This represents the most optimistic view and an upper bound, since undoubtedly some narrow-lined sources must be
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stellar in origin but masquerading as AGNs. The true space density of local AGNs most likely lies between these two possibilities. In either case, the differential luminosity function is reasonably well approximated by a single power law from M B M -5 to -18 mag, roughly of the form @ 0; L-1.2*o.2. The slope may flatten for M B 2 -7 mag, but the luminosity function is highly uncertain at the faint end because of density fluctuations in our local volume. For comparison, I have overlaid the luminosity function of z 5 0.3 quasars and Seyfert 1 nuclei as determined by Kohler et al. (1997) from the Hamburg/ESO UV-excess survey, scaled to the adopted cosmological parameters of Ho = 75 km s-' Mpc-l, R, = 0.3, and Ra = 0.7. This sample extends the luminosity function from M B M -18 to -26 mag. Although the two samples do not strictly overlap in luminosity, it is apparent the two samples roughly merge, and that the break in the combined luminosity function most likely falls near M g M -19 mag, where the space density $ M 1x MpcP3 magp1.
5. Radiative Inefficient Accretion
As Figure 4 shows, clearly the luminosities of most nearby nuclei are extremely low. To cast this statement in more physical terms, I have converted the optical luminosities to bolometric luminosities and then compared them relative to the Eddington luminosities, which were estimated from the black hole mass vs. velocity dispersion relation (Fig. 5 ) . Note that nearly all the objects have Lbol < erg s-l, and most significantly less. Seyferts are on average 10 times more luminous than LINE& or transition objects. More importantly, nearby nuclei are highly sub-Eddington systems. All One might argue that this objects have Lbol/LEdd < 1, with most < is to be expected. After all, in the present-day Universe bulge-dominated galaxies have spent most of their gas supply, leaving little fuel for central accretion. But this is not the whole story. It is true that not much fuel is needed to sustain the low level of activity observed. For a canonical radiative efficiency of 7 = 0.1 appropriate erg s-l requires only for a geometrically thin disk, Lbol = lo4' hi = l o p 6 - l o p 4 M a yr-l, ostensibly a minuscule amount. The trouble is that the innermost regions of early-type galaxies should have much larger gas reservoirs than this. Ho (2004, in preparation) estimates that Ma most galactic nuclei should have gas supplies as large as hi M yr-', predominantly coming from mass loss from evolved stars and Bondi
161 50
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Figure 5. Distribution of ( a ) nuclear bolometric luminosities and ( b ) Eddington ratios X E Lbol/LEdd. S = Seyferts, L = LINE&, T = transition objects, and A = absorptionline nuclei. Open histograms denote upper limits. (From Ho 2004b.)
accretion of hot gas. If this material were to be accreted and converted to radiation with 77 = 0.1, nearby AGNs should be much more spectacular that observed. This suggests that either only a tiny fraction of the available gas gets accreted or that 77 is much less than 0.1, as postulated in models of radiatively inefficient accretion flows (see Quataert 2001 for a review). If the gas is prevented from accreting, it is unlikely that supernova winds are the culprit, since there is little evidence of recent star formation in nearby nuclei (Ho et al. 2003). Instead, recent models of radiatively inefficient accretion flows suggest that these systems are naturally prone to generating winds or outflows, which would curtail the amount of material that actually gets accreted. Note, however, that this does not obviate the need for 77 to be small-only that it does not have to be as small as it would be in the absence of winds-because a radiatively inefficient flow is a precondition for establishing the winds. Nearby, low-luminosity AGNs are not simply scaled-down versions of luminous AGNs. As a direct consequence of their low accretion rates, most nearby AGNs do not have %tandard” optically thick, geometrically thin accretion disks. Instead, their central engines are more akin to the class of radiatively inefficient accretion flows discussed in the recent literature. Additional arguments in support of this picture can be found in Ho (2003).
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References 1. A.J. Barth, L.C. Ho, R.E. Rutledge & W.L.W. Sargent, ApJ in press (2004). 2. H. Baumgardt, P. Hut, J. Makino, S. McMillan & S. Portegies Zwart, A p J 582,L21 (2003a). 3. H. Baumgardt, J. Makino, P. Hut, S. McMillan & S. Portegies Zwart, A p J 589,L25 (2003b). 4. R. Bender, D. Burstein & S.M. Faber, ApJ 399,462 (1992). 5. L. Ferrarese & D. Merritt, ApJ 539,L9 (2000). 6. A.V. Filippenko & L.C. Ho, ApJ 588,L13 (2003). 7. A.V. Filippenko & W.L.W. Sargent, A p J 342,L11 (1989). 8. K. Gebhardt et al., A p J 539,L13 (2000). 9. K. Gebhardt, R.M. Rich & L.C. Ho, ApJ 578,L41 (2002). 10. M. Geha, P. Guhathakurta & R.P. van der Marel, A J 126, 1794 (2003). 11. J. Gerssen, R.P. van der Marel, K. Gebhardt, P. Guhathakurta, R.C. Peterson & C. Pryor, A J 124,3270 (2002). (Addendum: 2003, 125, 376) 12. J.E. Greene & L.C. Ho, ApJ submitted (2004). 13. L.J. Greenhill, J.M. Moran & J.R. Herrnstein, ApJ 481,L23 (1997). 14. L. Hao & M.A. Strauss, in Carnegie Observatories Astrophysics Series, Vol. 1: Coevolution of Black Holes and Galaxies, ed. L. C. Ho (Pasadena: Carnegie Observatories) (2004). 15. L.C. Ho in Active Galactic Nuclei: from Central Engine to Host Galaxy, ed. S . Collin, F. Combes, & I. Shlosman (San Francisco: ASP), 379 (2003). 16. L.C. Ho, ed., Coevolution of Black Holes and Galaxies (Cambridge: Cambridge Univ. Press) (2004a). 17. L.C. Ho, in Carnegie Observatories Astrophysics Series, Vol. 1: Coevolution of Black Holes and Galaxies, ed. L. C. Ho (Cambridge: Cambridge Univ. Press), in press (2004b). 18. L.C. Ho, A.V. Filippenko & W.L.W. Sargent, ApJ 487,568 (1997). 19. L.C. Ho, A.V. Filippenko & W.L.W. Sargent, ApJ583, 159 (2003). 20. L.C. Ho & C.Y. Peng, A p J 555,650 (2001). 21. S.A. Hughes, M N R A S 331,805 (2002). 22. G. Kauffmann et al., M N R A S in press (2004). 23. T. Kohler, D. Groote, D. Reimers & L. Wisotzki, A & A 325,502 (1997). 24. D. Kunth, W.L.W. Sargent & G.D. Bothun, A J 92,29 (1987). 25. C.J. Miller, R.C. Nichol, P.L. Gomez, A.M. Hopkins & M. Bernardi, ApJ 597, 142 (2003). 26. B. Moore, N. Katz, G. Lake, A. Dressler & A. Oemler, Nature 379, 613 (1996). 27. E. Quataert, in Probing the Physics of Active Galactic Nuclei b y Multiwavelength Monitoring, ed. B. M. Peterson, R. S. Polidan, & R. W. Pogge (San Francisco: ASP), 71 (2001). 28. A. Sandage & J. Bedke, The Carnegie Atlas of Galaxies, (Washington, DC: Carnegie Inst. of Washington) (1994). 29. S. Tremaine et al., ApJ 574,740 (2002).
AGNs IN THE MID-INFRARED
E. STURM Max-Planck-Znstitute for Extraterrestrial Physics (MPE) Giessenbachstr.1 85748 Garching, Germany E-mail:
[email protected] This contribution reviews some of the mid-infrared ( ~ 3 - 5 0 p m properties ) of AGNs as deduced recently from ISO-SWS observations of a large number of these types of galaxies. Mid-IR line ratio diagrams are presented, which can be used to idenAGN) sources and to distinguish between emission tify composite (starburst excited by active nuclei and emission from (circum-nuclear) star forming regions. Furthermore, correlations of mid-infrared line fluxes to the mid- and far-infrared continuum are used, in order to examine the contribution of AGNs to the infrared luminosities of their host galaxies. The ratio of mid-infrared AGN continuum luminosity to X-ray luminosity in Seyfert-1 and Seyfert-2 galaxies is presented as one way to test AGN unification theories. Finally, all these new diagnostics are applied to the infrared luminous galaxy NGC 6240, which played an important role at this conference as a prototype of highly obscured AGNs (QS02s, elusive AGNs).
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1. Diagnostics
1.1. Continuum and dust features
The continuum and broad band features of galaxies in the 5 - 15 pm range can be decomposed into three major components : (i) a component dominated by broad, aromatic dust emission features (‘PAHs’), arising in photo dissociation regions (PDRs) or the diffuse interstellar medium of the host, (ii) an HI1 region continuum rising steeply towards wavelengths beyond 10pm, and, (iii) for active galaxies, a typically flatter, warmer, PAH-free AGN continuum (Figure 1 left). The shape of the continuum in combination with the relative strength of the PAHs allows a classification of galaxies as starburst or AGN driven even with low resolution spectra (e.g. Laurent et al. 2000). In cases of good signal-to-noise ratio and full wavelength coverage (5-15 pm), it is possible to derive a full spectral decomposition and to quantify possible AGN continua using template spectra accounting for all the effects mentioned above (e.g. Tran et al. 2001; Spoon et al. 2001). 163
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In extremely obscured sources, high-S/N (low-resolution) spectra will also show absorption features of ices, silicates, and hydrocarbons, mainly in the 6-8 pm range (e.g. Spoon et al. 2002). These features can trace deeply embedded AGNs or highly obscured, compact starbursts.
Figure 1. Left: ISOCAM-CVF example spectra for typical HII, PDR, and AGN spectra in the 5 to 16 pm range (Laurent et al. 2000). Right: Separation of the mid-IR spectrum of NGC 6240 into a starburst component (M82, i.e. PDR plus HII) and an obscured AGN continuum, from Lutz et al. 2003.
1.2. Emission Lines The mid-IR fine structure line spectrum of galaxies contains tracers of low excitation gas (HI1 region) and high excitation gas (AGN NLR) as well as partially ionized zones (AGNs, shocks). An example of a mid-infrared diagnostic diagram that can be used to distinguish between photoionization by AGNs as opposed to hot stars is shown in Figure 2 (left). Sturm et al. (2002) have developed such mid-infrared fine structure diagnostic diagrams (also employing, e.g. [0IV] and [Fe II]), as mid-IR analogues of the traditional optical ones (e.g. Veilleux & Osterbrock 1987). Key advantages of mid-IR line ratios are generally small extinction corrections and insensitivity to electron temperature variations. The role of shocks as ionization sources can be probed by the relative strength of shock tracers like [Fe 111 26pm. This line is strong in IS0 spectra of starbursts and supernova shocks (SNRs), but (relatively) weak in AGNs, compared to [0IV] 25.9pm (Lutz et al. 2003). Figure 2 (right) shows another example of a mid-IR line ratio diagram which combines these principles in order to separate star formation, AGN, and shocks. The
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position of a source in such a diagram is driven by the relative contributions from these different mechanisms. 1
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Figure 2. Left: A mid-IR diagnostic diagram to distinguish starbursts from AGN in dusty galaxies (Sturm et al. 2002). AGNs are shown as diamonds, starburst galaxies as stars. The supernova remnant shock source RCW 103 is displayed as a triangle. Circles around symbols indicate composite objects for which contributions from both stars and AGN are present within the aperture. Right: A second example of a diagnostic plot separating star formation, AGN, and shock excitation via mid-IR fine structure lines (Lutz et al. 2003). The position of the ULIRG NGC6240, shown as a triangle, indicates a strong contribution from stars, but also a non-negligible fraction from an AGN and from shock zones (Lutz et a1.2003).
The high excitation lines like [0IV], [NeV], or [NeVI] in Seyfert galaxies are well correlated with the mid-to-far IR continuum radiation. Low ionization lines, which might have significant contributions from circumnuclear star formation, show similar correlations (Genzel et al. 1998, Sturm et al. 2002). In particular the [NeIII-to-FIR correlation is very similar in both Seyfert and starburst galaxies, over a large range of the infrared luminosity (Fig. 3 left). This makes [NeII] 12.8pm a valuable reference line for comparisons of line ratios in different sources. One example of a diagnostic diagram resulting from this principle is shown in Fig. 3 (right). The [OIV]25.9pm/[NeII] ratio does not drop below 1 in pure Seyfert spectra, while it reaches values of at most a few times 0.01 in starburst galaxies. 2. Applications
We have used the constancy of the [Ne111-to-FIR ratio to construct simple linear mixing models of AGN contribution to the infrared luminosities of composite sources for the ratio [0IV]/[Ne 111 based on it's mean values in pure starbursts and pure AGNs. As can be seen from the right-hand yaxis of Fig. 3 (right) composite sources lie in the 10 to 50 percent domain
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Figure 3. Left: [NeII] luminosity vs. FIR luminosity for AGNs (diamonds), starburst galaxies (stars), and composite sources (triangles). Right: The ratio [0IV]25.9pm/[Ne II]12.8pm, for Seyfert-1s (diamonds), Seyfert-2s (asterisks), and the starburst prototype M 82 (triangle). Composite objects are encircled. Denoted on the right hand y-axis is a simple linear 'mixing' model of AGN contribution to the infrared luminosity (Sturm et al. 2002).
of these mixing curves. When applying such simple models to individual sources one should keep in mind that there is some scatter in the underlying relations, and the derived contributions in percent should not be taken too literally. For statistical studies, however, these models provide a valuable means of quantifying the AGN contribution to the luminosity of dusty, composite objects. Lutz et al. (2004) have applied a variation of the decomposition technique for low resolution spectra to a large sample of Seyfert galaxies to compare the mid-IR luminosities of the isolated AGN continua t o the hard X-ray luminosities, which are considered tracers of the bolometric luminosity of the central AGN. Because the AGN emission is reprocessed by dust, either in the putative torus or on somewhat larger scales inside the Narrow Line Region (NLR), the observed mid-infrared emission is a function not only of the AGN luminosity but also of the distribution of the obscuring matter and of the viewing direction of the observer: radiative transfer models of the emission from a geometrically and optically thick torus (e.g. Nenkova et al. 2002 and references therein) predict a strong anisotropy of the mid-infrared emission. In this case the unified model predicts for type-2 galaxies a lower ratio of mid-infrared emission and (absorption corrected)
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X-ray emission. The study by Lutz et al. (2004) has confirmed the expected relation between mid-infrared and X-ray emission, however with a relatively large scatter and without the expected difference between Seyfert 1 and Seyfert 2 continuum strength (Fig. 4). This is most probably due to significant non-torus contributions to the AGN mid-IR continua.
Figure 4. Hard X-ray luminosities (corrected for absorption) vs. 6pm AGN continuum luminosities for Seyfert-1s (diamonds) and Seyfert-2s (asterisks). See Lutz et al. (2004).
3. Highly obscured AGNs - the case of NGC 6240 More and more galaxies are being found now whose optical and nearinfrared properties reveal no evidence for an AGN, but whose X-ray observations clearly prove the presence of a powerful and heavily obscured AGN (e.g. the “elusive” AGNs of Maiolino et al. 2003). Such heavily obscured AGNs may play an important role for the cosmic X-ray and infrared backgrounds, as well as type-2 QSO candidates (e.g. Norman et al. 2002). One possible reason for their normal appearance in optical and near-infrared could be that the NLR is heavily obscured along our line of sight. Alternatively, the nuclear ionization source itself could be covered in all directions (rather than by a torus-like structure), such that no NLR is produced at all. A famous representative of this class of heavily obscured
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AGNs is NGC 6240, a nearby infrared luminous system which is often used as a template for luminous type 2 AGNs (QS02s, e.g. Norman et al. 2002) or “elusive” AGNs (Maiolino et al. 2003). What do the mid-IR diagnostics tell us? Fig. 1 (right) shows the decomposition of the mid-IR continuum of NGC6240 (Lutz et al. 2003). The comparison t o spectral templates reveals, that a starburst component alone does not fit the observed continuum. There is a significant contribution from an obscured, warm AGN continuum. In the mid-IR/X-ray relation (Fig. 4) NGC 6240 displays a low mid-IR continuum relative t o its X-ray luminosity, pointing t o a high obscuration of the 6pm continuum. The [OIV]/[NeII]ratio (Fig. 2 left) lies in the range of composite objects with x 10 % ’ AGN contribution. Finally, the position of NGC 6240 in Fig. 2 (right) identifies this galaxy as mostly starburst driven, but again with a significant contribution from an AGN (plus an enhanced importance of shocks). Clearly, [0IV] is much stronger than in starburst galaxies, and is consistent with the NLR of normal Seyfert galaxies. Obviously, in this case the NLR is not entirely obscured, at least not in the mid-IR. A similar study for a larger sample of obscured AGNs is left t o the Spitzer Space Telescope.
Acknowledgements Much of my own work presented here was obtained in collaboration with Reinhard Genzel, Dieter Lutz, Alan Moorwood, Hagai Netzer, Amiel Sternberg, Linda Tacconi, Aprajita Verma and many others over the course of many years.
References 1. R. Genzel et al., ApJ498, 579 (1998). 2. 0. Laurent et al., A B A 359, 887 (2000). 3. D. Lutz et al., A B A 409, 867 (2003). 4. D. Lutz et al., A B A in press (2004). (astro-ph/0402082) 5. R. Maiolino et al., M N R A S 344, L59 (2003). 6 . M. Nenkova, 2. IveziC & M. Elitzur, A p J 570, L9 (2002). 7. C. Norman et al., A p J 571, 218 (2002). 8. H.W.W. Spoon et al., A B A 365, L356 (2001). 9. H.W.W. Spoon et al., A B A 385, 1022 (2002). 10. E. Sturm et al., A B A 358, 481 (2000). 11. E. Sturm et al., A B A 393, 821 (2002). 12. D. Tran et al., A p J 552, 527 (2001).
RADIO PROPERTIES OF LOCAL AGN
N. M. NAGAR* Kapteyn Institute Landleven 12, 9’74’7A G Groningen The Netherlands E-mail:
[email protected] H. FALCKE A S T R O N , Dwingeloo, The Netherlands
A. S. WILSON Astronomy Department, University of Maryland, USA.
This article focuses on the radio properties of the -470 nearby bright (northern) galaxies of the Palomar spectroscopic sample. Almost half the sample’s galaxies have nuclei with emission-lines characteristic of AGN but with L H 5 ~ 1040 erg s-l. These are referred to as low-luminosity AGNs or LLAGNs. The power source of such LLAGNs has been long debated. High resolution radio surveys of the sample - with the VLA at 15 GHz (150 mas resolution), and the VLBA at 5 GHz (2 mas resolution) - have now revealed a high incidence of pc-scale radio cores with implied brightness temperatures 2 los K, and sub-parsec scale jets. The results support the presence of accreting black holes in 250% of all LLAGNs; there is no evidence against all LLAGNs being mini-AGNs. The detected parsec-scale radio cores are almost exclusively found in massive ellipticals and in type 1 (i.e. with broad Ha: emission) nuclei. These nuclei follow the usual correlations between radio and emission-line gas properties found in more powerful AGNs. The radio luminosity function (RLF) of Palomar Sample LLAGNs extends three orders of magnitude below, and is continuous with, that of ‘classical’ AGNs. We find marginal evidence for a low-end turnover in the RLF; nevertheless LLAGNs are responsible for a significant fraction of accretion in the local universe. Low accretion rates (5 lop2of the Eddington rate) are implied in both advection- and jet-type models. Within the context of jet models, the accretion energy output is dominated by the energy in the jet rather than the radiated bolometric luminosity. These jets would be able to dump sufficient energy into the innermost parsecs to significantly slow the accretion inflow. Detailed results can be found in Nagar et al. 2002; 2004 and references therein.
*Work partially supported by NWO and the Kapteyn Institute, Netherlands.
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1. Introduction
The debate on the power source of low-luminosity active galactic nuclei (LLAGNs, i.e. low-luminosity Seyferts, LINE&, and "transition" nuclei [nuclei with spectra intermediate between those of LINE& and H 11 regions]) is a continuing one. Their low emission-line luminosities (LH, 5 lo4' erg s-l by definition; Ref 27) can be modeled in terms of photoionization by hot, young tar^,^^^^^^^^ by collisional ionization in shocks34~20~23~12 or by aging starbursts.' On the other hand, evidence has accumulated that a t least some fraction of LLAGNs share characteristics in common with their more powerful counterparts - radio galaxies and powerful Seyfert galaxies. These similarities include the presence of compact nuclear radio cores,23 water vapor mega maser^,^ nuclear point-like UV source^,^^^^ broad H a lines,28 and broader H a lines in polarized emission than in total e m i ~ s i o nIf. ~LLAGNs are truly scaled down AGNs then the challenge is to explain their much lower accretion luminosities. This requires either very low accretion rates of the Eddington accretion rate, L ~ d d or ) radiative efficiencies (the ratio of radiated energy to accreted mass) much lower than the typical value of ~ 1 0 % (e.g. Chapter 7.8 of Ref 21) assumed for powerful AGNs. One well-known property of some powerful AGNs is a compact (subparsec), flat-spectrum nuclear radio source, usually interpreted as the synchrotron self-absorbed base of the jet which fuels larger-scale radio emission. Astrophysical jets are known to be produced in systems undergoing accretion onto a compact o b j e ~ t so ~ ~such ? ~ compact radio sources in galactic nuclei may reasonably be considered a signature of an AGN. Much theoretical ~ ~ r khas ~been' devoted ~ ~ to , this ~ disk-jet ~ relationship in the case of galactic nuclei and it has been suggested that scaled-down versions of AGN jets can produce flat-spectrum radio cores in LLAGNs.14 Compact nuclear radio emission with a flat to inverted spectrum is also expected from the accretion inflow in advection-dominated (ADAF) or convectiondominated (CDAF) accretion Flat-spectrum radio sources can also result through thermal emission from ionized gas in normal H 11 regions or through free-free absorption of non-thermal radio emission, a process which probably occurs in compact nuclear starbursts." The brightness temperature, T b , in such starbursts is limited to log [ T b (K)] 55 (Ref 10). Thus it is necessary t o show that Tb exceeds this limit before accretion onto a black hole can be claimed as the power source. From the observational perspective, LINER nuclei tend to be asso(W
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ciated with a compact radio source,23 and compact, flat-spectrum radio . ~ ~ ~ ~ ~ cores are known t o be present in many 'normal' E/SO g a l a x i e ~Flatspectrum radio cores are, however, uncommon in normal spirals or Seyfert g a l a ~ i e s , though ~ ~ t ~ ~low-luminosity Seyferts show a higher than usual incidence of flat-spectrum cores.55 The radio regime offers several advantages for identifying (mini-)AGNs. Gigahertz (cm wave) radiation does not suffer the obscuration that affects the UV to infra-red. Also, at tens of gigahertz the problems of free-free absorption can be avoided in most cases. Finally, high resolution, high sensitivity radio maps can be routinely made with an investment of less than an hour per source at the Very Large Array (VLA) and the Very Long Baseline Array (VLBA). At their resolutions of -100 milli-arcsec (mas) and -1 mas, respectively, it is easy to pick out the AGN, since any other radio emission from the galaxy is usually resolved out.
2. Sample and Radio Observations
We focus on LLAGNs in the Palomar spectroscopic survey of all (-470) northern galaxies with BT < 12.5 mag.27 Spectroscopic parameters (including activity classification) of 403 galaxies in the sample which show nuclear emission lines have been presented in [27]. Of these, roughly 7 are AGNs, roughly 190 are LLAGNs, and 206 have H 11 type nuclear spectra. Earlier surveys24~30~33~31~58~32~13~8~5g~36 have targeted a substantial fraction of the nearby galaxies now in the Palomar Sample. Since the publishing of comprehensive optical results on the Palomar Sample, three groups have conducted large radio surveys of the sample. We41116943t44have observed 162 LLAGNs with the A-configuration VLA at 15 GHz (2 cm; 150 mas resolution, with 100 detection limit 1.0-1.5 mJy). This comprises all LLAGNs in the sample except some transition nuclei at D > 19 Mpc. We then followed up 27 LLAGNs with the VLBA at 5 GHz (6 cm; resolution -2 mas; 10a detection limits of 1.5 mJy to 2 mJy). Ref 29, 55, 2 have observed all (45) Seyfert galaxies in the sample at arcsec-scale resolution a t 6 cm and 20 cm and followed up some of the strong detections a t multiple frequencies with the VLBA. Ref 17, 18 have completed a 5"-0?3 resolution survey of all transition nuclei in the sample with follow up VLBA observations of some of the stronger nuclei. Finally, radio cores at the levels of those in LLAGNs were not detected in any of 40 H 11 type nuclei in the sample,56justifying their exclusion from the remaining discussion here. Together with data from the literature, this completes sub-arcsecond VLA observations of all
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except four LLAGNs and AGNs in the Palomar sample, and high resolution VLBA or VLBI observations of all LLAGNs and AGNs from the Palomar sample with Syk$Hz > 2.7 mJy. Of the additional nearby galaxies observed in our project (selected for having accurate black hole mass estimates) NGC 205, NGC 7457, and NGC 7768, were detected at a level of -1.2 mJy with the VLA Aconfiguration, while the remaining galaxies NGC 221, NGC 821, NGC 1023, NGC 2300, and NGC 7332, were not detected at a 10a limit of 1.5 mJy.
3. Results Tabular compilations of the results appear in Nagar et al. 2002 and Nagar et al. 2004. The VLA detection rates (Fig. 1) are -50% for LINE% and Seyferts - the detected nuclei are preferentially type 2 LLAGNs in massive % transition nuclei are detected; ellipticals or type 1 LLAGNs. Only ~ 1 0 of these detections are in nuclei closest to the cutoff between transition nuclei and LINERs/Seyferts. We are confident of the nuclear origin of the radio emission since the radio position closely matches that of the optical galaxy nucleus.” The follow up milli-arcsec resolution imaging of all nuclei with > 2.7 mJy detected 42 of 43 observed LLAGNs and AGNs; implied brightness temperatures are ?lo8 K.
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Figure 1. Detection rate of 15 GHz 150 mas-scale radio nuclei for “L”INERs, “S”eyferts, “T”ransition, and H 11 nuclei in the Palomar sample. Note the higher detection rate of type 1 (with broad H a emission) nuclei.
Nuclear starbursts can have a maximum brightness-temperature of 104-5K (Ref 10) while the most luminous known radio supernova remnantsg would have brightness temperatures I l o 7 K even if they were 5 1 pc in extent. If the nuclear radio emission is attributed to thermal processes, the predicted soft X-ray luminosities would be a t least two orders of magnitude higher16 than observed.51>26952918 Also, as discussed in N
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Ref 55, a single SNR or a collection of SNRs would have radio spectral indices different from those observed. Thus, the only currently accepted paradigm which may account for the mas radio cores is accretion onto a supermassive black hole. In this case, the mas-scale radio emission is either emission from the accretion inflow45or synchrotron emission from the base of the radio jet launched by the accreting supermassive black hole.14760 Many of the nuclei have sub-parsec scale (and sometimes larger scale) 'jets' (some examples in Fig. 2). Interestingly, these LLAGNs belong in one of three groups: radio or mini-radio galaxies with sub-pc to kpc jets, nuclei with no detected sub-pc jet but detected 100 pc-scale jets (usually Seyferts), and nuclei with sub-pc jets but not larger scale jets (typically LINERs).
Figure 2. E ~ a r n p l e s ~of" ~ 5 ~G ~H z VLBA maps of nuclei with pc-scale jets; (left to right) N G C 2273,NGC 4552, NGC 4589, N G C 5363,and N G C 7626.
3.1. Radio Power and Emission-Line Luminosity
These correlations have been addressed in detail for the Palomar At the upper end of the radio luminosity and emission-line luminosity, the Palomar LLAGNs are similar to radio galaxies and 'classical' Seyfert galaxies, respectively. At the lower luminosity end the picture is not so clear, though the LINERs (mostly those in elliptical galaxies) tend to follow the low-luminosity extrapolation of powerful radio galaxies. 3 . 2 . Radio Luminosity and Black Hole Mass
This issue has been discussed in detail using all the radio data presented here.43 Fig. 3 shows the relation between radio power and black hole mass for the Palomar LLAGNs and several other nearby galaxies. Linear regression analysis on all (73) galaxies with radio fluxes measured a t cm-2. The detailed investigation of nearby cases, in which these effects can be spatially and spectrally disentan*Also Code 662, NASA/GSFC, Greenbelt, MD 20771, USA
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gled, is valuable to quantify the properties of the building blocks that are present in more distant and more luminous examples, where such detailed study is impossible. 2. Case Study: NGC 7130 NGC 7130 serves as a case study. Classified on the basis of optical emission line ratios, it is a normal Seyfert 2,5and it also contains a powerful compact circumnuclear starburst.2 NGC 7130 is nearby ( D = 69 Mpc; 1" = 330 pc), allowing detailed analysis. Both the starburst and the AGN are energetically important, even in the X-ray regime.
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Stellar processes are entirely responsible for the large-scale (15 kpc) extended emission in the Chandru observation of NGC 7130, and we must spatially and spectrally isolate the AGN to measure it accurately. Even in the spectrum of the central 1!'5 (Fig. l), the nuclear starburst is evident as strong, soft (kT = 0.65) thermal emission. The AGN is not detected
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directly in this Compton thick example. Although its intrinsic spectrum is expected t o be described by a power law of photon index I? M 1.9, the continuum emerges only when reprocessed to r = 0 and diminished by a factor of We use the prominent iron K a line, with equivalent width EW = 1.2 keV, t o estimate the intrinsic luminosity of the buried AGN (Fig. 2) *
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log v (Hz) Figure 2. Spectral energy distribution of NGC 7130, showing largescale emission (open points) and the spatially isolated AGN contributions (filled points). As a whole, the For comparison, galaxy appears very similar to dusty starburst galaxies (solid the average radio-quiet quasar spectrum' scaled to the intrinsic bolometric luminosity of NGC 7130 is shown (dotted line).
NGC 5135 is another example of a Compton thick AGN coincident with a circumnuclear starburst. Similar t o NGC 7130, both the central and extended star formation are responsible for most of the observed soft X-ray flux.4 The buried AGN accounts for most of the hard X-rays, but the emergent flux is orders of magnitude less than its intrinsic power.
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3. Hardness Ratios Even obscured AGN are often bright enough t o detect in deep X-ray surveys, but their properties can be misdiagnosed with limited information. The most common simple characterization uses an X-ray hardness ratio t o determine both the degree of obscuration and the intrinsic luminosity. This is an appropriate measurement if the buried AGN dominates the total Xray emission and is detected directly in the hard X-ray bandpass. In such instances, the lack of soft X-ray emission accurately indicates the absorption while allowing direct measurement of the true AGN power at higher energies. The case studies here illustrate the limitations of this technique, however. In both NGC 7130 and NGC 5135, the hardness ratio of the entire galaxy is soft because even the intrinsic hard AGN emission is suppressed and the stellar contribution enhances the soft flux. The crude measurement would mistakenly indicate a weak and lightly-absorbed AGN in each case, rather than the powerful fully-blocked central engine that is present. The AGN luminosity does emerge at far-infrared and very hard X-ray energies (above 10 keV), with important consequences for the study of ultra-luminous infrared galaxies and the cosmic X-ray background. The question in the former is whether star formation or accretion is the primary energy source. NGC 7130 and NGC 5135 empirically demonstrate that star formation can be overwhelmingly responsible for the measurable emission, even when an active nucleus is present in a normal galaxy. The second issue is that deep surveys successfully resolve most of the X-ray background below 10 keV, but their sources do not successfully reproduce the spectrum at higher energies. A population of Compton thick AGN is essential, and these nearby case studies demonstrate why they are not evident from simple X-ray diagnostics alone.
References 1. M. Elvis et al., ApJS 95, 1 (1994). 2. R.M. GonzAlez Delgado, T. Heckman, C. Leitherer, G. Meurer, J. Krolik, A.S. Wilson, A. Kinney & A. Koratkar, A p J 505, 174 (1998). 3. J.H. Krolik, P. Madau & P. T. Zycki, ApJL 420, L57 (1994). 4. N. A. Levenson, K.A. Weaver, T.M. Heckman, H. Awaki & Y. Terashima, A p J 602, 135 (2004). 5. M.M. Phillips, P.A. Charles & J.A. Baldwin, A p J 266, 485 (1983). 6. H.R. Schmitt, A.L. Kinney, D. Calzetti & T. Storchi Bergmann, A J 114, 592 (1997).
USING THE X-RAY EMISSION LINES OF SEYFERT 2 AGN TO MEASURE ABUNDANCE RATIOS
M. A. JIMENEZ-GARATE AND T. KHU* MIT Center for Space Research, 70 Vassar St., NE80-6009 Cambridge, M A , 02139, USA. E-mail:
[email protected] We measure the metal abundance ratios in the X-ray photoionized gas located near the narrow line region of a sample of Seyfert 2 AGN. The high-resolution Xray spectra observed with the Chandra high- and low-energy transmission grating spectrometers are compared with models of the resonant scattering and recombination emission from a plasma in thermal balance, and with multiple temperature zones. The abundance ratios in the sample are close to the Solar values, with slight over-abundances of N in NGC 1068, and of Ne in NGC 4151. Our X-ray spectral models use fewer degrees of freedom than previous works.
Motivation. Our goal is to use X-ray abundance measurements to cross-calibrate with the optical spectra of quasars. These optical spectra are used to measure the star formation history of the early Universe.' To Determine the Abundance Ratios, we fit the Seyfert 2 spectra with models of photoionized plasmas, and then search for deviations in the data from Solar abundances, as shown in Fig. 1. The fluxes of radiative recombination continuum (RRC) features and the radiative recombination (RR) forbidden lines depend little on radiation transfer effects, so they are the most reliable abundance indicators. At low continuum optical depths, the recombination emission flux scales linearly with abundances. Our model allows us to fit the RRC and RR fluxes by accounting for the broad ionization distribution in the plasma. X-ray Emission Line Model. We model a photoionized plasma in ionization equilibrium and thermal balance with a grid of zones, each with ionization parameter logc = 1.0,1.5,...4.5 (in c.g.s. units). The XSTAR plasma code yields the charge state distribution of each zone.' In order to calculate the recombination emission, we use the photoelectric cross sections 'This work was supported by NASA contract NAS 8-01129.
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from Ref. 3, and the recombination rates calculated with the HULLAC atomic code,4 provided by Ref. 5. To calculate the resonance line fluxes, we use the oscillator strengths from Ref. 6. We assume the ionizing spectrum of a radio-quiet q ~ a s a rwith , ~ an X-ray power-law and high-energy exponential cutoff. We assume a power-law distribution of column density as a function of E , so N H ( < )0: (log,,c)fl, with ,O a free ~ a r a m e t e r The . ~ advantages of this model are that 1) it provides a simple fit to the ionization distribution, 2) it has only five free parameters, instead of the several dozen parameters in other models,s and 3) it uses accurate atomic data. Conclusion. The abundances in NGC 1068, NGC 4051, and NGC 4507 do not deviate much from the Solar values. Nitrogen is over-abundant by a factor of 5 2 in NGC 1068, and neon is over-abundant in NGC 4051. There are no signatures of starburst activity. Further work is needed to quantify the systematic and statistical errors, and to compare with optical spectra.
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Figure 1. A portion of the X-ray spectrum of NGC 1068 measured with the Chandra high-energy transmission grating (grey), and model fit (black).
References F. Hamann & G. Ferland, ARA&A 37, 487 (1999). T.R. Kallman & R. McCray, ApJ 50,263 (1982). D.A. Verner & D.G. Yakovlev, A&AS 109,125 (1995). M. Klapisch et al., Opt. SOC.Am. 61,148 (1977). D.A. Liedahl, private communication (2001). D.A. Verner, E.M. Verner & G.J. Ferland, Atomic Data Nucl. Data Tables 64, 1 (1996). 7. M. Elvis et al., A p J S 95,’ 1 (1994). 8. A. Kinkhabwala et al., ApJ 575,732 (2002). 9. M.A. Jimenez-Garate et al., ApJ 578,391 (2002).
1. 2. 3. 4. 5. 6.
EXTINCTION CURVE TOWARD THE NUCLEAR REGION OF M82
L. HERNANDEZ-MARTINEZ I A UNAM, Circuit0 Exterior, Ciudad Universitaria, 0.451 0 M&xico, D. F. E-mail:
[email protected] D. MAYYA INAOE, Luis Enrique Erro 1, C.P. 72480, Sta. Man'a Tonantzintla, Puebla, Mixico. E-mail:
[email protected] We report on the determination of the extinction curve (EC) toward a 30 pc dust spot in the nuclear region of M82. The curve is based on optical spectra of two adjacent regions at 100 and 200 pc distance respectively on the south-west side of the nucleus. The spectra of the two regions seem identical except that one region is experiencing a higher visual extinction than the other (AA, N lmag). We find that the resulting curve is in close agreement with that derived by [l]for a sample of nuclear star-forming galaxies over kiloparsec scales.
1. Description of the method and results In this study, we make an attempt to determine the extinction curve (EC) using a dust feature, which seems to cross at 100 pc south-west of the starburst center of M82. Our aim is to check whether the EC defined by [l]over kilo-parsec scales is applicable over spatial scales smaller than 100 pc. Long-slit, low resolution ( w lOA) spectra of M 82 nucleus covering 35009600 A, were taken during 1999 February at the Guillermo Haro Astrophysical Observatory, Cananea, Mexico. The slit of 1.6" width, placed at a position angle of 62", passes through the optically bright center of M82, a dust feature and region C [3], denoted by letters A, D and C, respectively in Figure 1 (left). F' IF' k ~-2.51og (+F), where The EC k ( X ) is defined by (A,,, - A w x 2 ) = FA,/F,Z AWA,F i and F: are respectively, the visual extinction, the observed and intrinsic spectra of regions C (suffix 1) and D (suffix 2). The derivation of the EC is based on the assumption that the intrinsic spectra of C and 193
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D are identical. The K-band image of this region is smooth without any separation between C and D, which is the basis of our assumption. We fixed the ratio ( F ~ , / F ~so o )as to have k5500 = 1. The resulting points, along with the rms errors in line-free sampling windows of l O O A width, are plotted in Figure 1 (right). The large error bars at X < 4000A are due to the faintness of the observed spectrum there due to a combination of higher extinction and lower quantum efficiency of the detector at bluer wavelengths. It can be seen from the figure that the Calzetti et al. EC is in better agreement with the M82 EC than the galactic EC. At X > 8000A, the bright K-nucleus is probably contaminating the spectrum of the region D, and hence the EC derived by us is not reliable. ,
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Figure 1. HST image of the nuclear region of M82 (left), showing the position of our slit (diagonal line), the starburst center (A), the dust feature (D) and region (C). On the right, the derived extinction curve (symbols) is shown along with Calzetti et al. EC (solid line) and the Galactic EC as defined by [2](dotted line).
2. Concluding remarks
The presence of a dust feature of 30 pc size obscuring a star-forming region between 100-200 pc from the nucleus of M 82 has allowed us to determine the EC by a direct method. The derived EC agrees well with that derived by Calzetti et al. (1994) for kiloparsec-scale star-forming regions, in the 3500 to 8000A spectral region. The dust causing the extinction belongs to the well-known molecular torus of M82. Hence Calzetti et al. EC is applicable to scales smaller than 100 pc, typical size of the dust associated with the molecular torus around AGNs. References 1. D. Calzetti, A.L. Kinney & T. StorchiBergmann, ApJ 429, 582 (1994). 2. J.A. Cardelli, G.C. Clayton & J.S. Mathis, ApJ 345, 245 (1989). 3. R.W. O’Connell & J.J. Mangano, ApJ 221,62 (1978).
THE AGN PAIR NGC 5953/54: BVRIHaJK PHOTOMETRY AND [NII] FABRY-PEROT INTERFEROMETRY*
H. M. HERNANDEZ-TOLEDO, I. CRUZ-GONZALEZ, I. FUENTES-CARRERA, M. ROSADO, A. FRANCO-BALDERAS AND D. DULTZIN-HACYAN Instituto de Astronoma'a, UNAM. Apartado Postal 70-264,CP 04510 MLxico, D.F., Mkxico E-mail:
[email protected] New BVRIHaJK imaging and [N 111 scanning Fabry-Perot (OAN-SPM) observations are presented for the interacting galaxy pair NGC 5953/54. Morphology is reviewed and complemented by archived V/R/H images from HST. The Seyfert 2 NGC 5953 shows an underlying featureless disk (2 1.5 kpc) in all the observed 60 pc bar-like bands. A compact flocculent spiral pattern ( 5 1.5 kpc), and a central structure are observed. The Liner galaxy NGC 5954 is a distorted spiral with a strong circumnuclear starburst region and star-forming regions distributed throughout its disk. A tidal bridge or distorted arm appears to link the two galaxies, extending to the northwest as a linear feature (plume). Fabry-Perot observations yield a [N 111 velocity field and rotation curves for the components. These observations coupled with results from a simulation atlas of tidal features allow us 1) to suggest a tentative geometry of the encounter and 2) to comment about a suspected secular transformation in NGC 5953/54 via the interaction process. N
1. NGC 5953/54: A pair of mutually triggered AGNs?
In this contribution we emphasize that any connection between nuclear activity and interactions is likely to involve variables such as the geometry of the encounter and its role to control the fueling efficiency during the interaction, the intrinsic structure (bulge/disk mass ratio) of the intervening galaxies, the stage of the encounter and the time scales involved. With those ideas in mind, and taking into account our kinematic results, we start exploring a probable geometry of the encounter in NGC 5953/54. The scenario emerging from matching the observed morphology to simula*Based on observations with the 1.5 and 2 . l m telescopes of the OAN in San Pedro M k t i r , B. C., MBxico.
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tions (Howard et al. 1993) emphasizes the fundamental role that both the interaction geometry and the intrinsic structure of the intervening galaxies can play in the morphological transformation of NGC 5953/54 a. Figure 1 shows a review of some of the most important morphological features detected in NGC 5953/54 in our multi-wavelength study.
Figure 1. A B-band contrast/enhanced image showing a schematic representation of the observed features in NGC 5953/54. The scale of the image is 0.13 kpc per arcsec 5.8 kpc. A zoom of the inner regions of yielding a projected apparent separation of NGC 5953 is shown as seen from HST WFPC2 (V/R-band).
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References 1. S.A. Howard, W.C. Keel, G.G. Byrd, & J.M. Burkey, ApJ417, 502 (1993). 2. H.M. HernBndez-Toledo et al., A&A 412,669 (2003). ~~
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aA more detailed discussion of all our observations can be found in Hernhdez-Toledo et al. (2003)
STATISTICAL PROPERTIES OF HIGH-IONIZATION FORBIDDEN EMISSION LINES OF SEYFERT GALAXIES
T. NAGAO, T. MURAYAMA AND Y. TANIGUCHI Astronomical Institute, Graduate School of Science, Tohoku University Armaki, Aoba, Sendai 980-8578, Japan;
[email protected]. ac.jp Based on the statistical analysis of narrow emission-line flux ratios of various types of AGNs, physical properties and geometrical configurations of narrow-lineregions in AGNs are investigated.
HINERs Inferred by the Type Dependences of Forbidden Line Fluxes. In order t o investigate the physical properties and geometrical configuration of narrow-line regions (NLRs) in AGNs and to construct realistic multi-zone photoionization models for NLRs, we analyzed various narrow emission-line flux ratios, which is compiled from the literature. It is then found that forbidden lines with a high ionization potential (e.g., [Ne ~1x3426and [Fe ~1x6374)and/or a high critical density (e.g., [Ne III]x3869 and [0III]x4363) tend to be stronger in type 1 AGNs than in type 2 AGNs, although there is no systematic difference in the fluxes of forbidden lines with a low ionization potential and a low critical density. This can be naturally understood by introducing a highly-ionized dense component which is located so close to the central engine that it is obscured when seen from an edge-on toward the dusty torus, as previously proposed by Murayama & Taniguchi (1998). To examine the physical properties of this high-ionization nuclear emission-line region (HINER) , we carry out a dual-component photoionization model calculation in which the HINER component and a rather low density, typical NLR clouds are taken into account. We use the publicly available code Cloudy ver.94.0 (Ferland 1997). As a result, we obtain the lower limit of the gas density and the ionization parameter of the HINER component; TIHINER > lo6 cmP3 and UHINER> (Nagao et al. 2001a). Are There Dust Grains in HINERs? It is known that a low-ionization outer part of NLRs contains dust grains, which significantly affects emission-line spectra in several ways. Thus, to interpret 197
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high-ionization emission-line spectra correctly, it is important to examine whether or not dust grains survive also in the HINERs. We then focus on [Fe ~11]X6087 and [Ne ~1x3426,which have similar ionization potentials and critical densities. This is because their flux ratio is insensitive to the physical parameters but sensitive to the elemental abundance ratios of Fe and Ne, which is determined mainly by the abundance of dust grains. Based on the dual-component photoionization model calculations, it is shown that iron is not depleted onto dust grains in HINERs, implying that the HINER is not dusty. This result is consistent with the picture of the dual-component NLR model in which the HINER is located closer than the dust-sublimation radius (i.e., the inner radius of dusty tori) and thus is hidden by dusty tori when seen from an edge-on view toward the tori (Nagao et al. 2003).
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Figure 1. Left: Compiled data are compared with the results of the dual-component photoionization model calculations (see Nagao et al. 2001b for more details). Black and white circles denote type 1 and type 2 AGNs, respectively. The fraction of the contribution from HINERs (here ~ H I N E R= lo7 cmT3 is adopted) in the [0III]X5007flux is also shown. The density of the outer low-ionization NLR is assumed to be ~ Z H I N E R= lo1, lo2, lo3, lo4, lo5, and lo6 ~ m - ~The . data points will move on the diagram as shown by the arrow if the extinction correlation of A" = 1.0 mag is applied. Right: Same as the left figure but for the diagram of [Fe v11]/[01111 vs. [Ne v]/[O 1111. The plotted models are the results of the dual-component photoionization model calculations with and without dust grains. The ionization parameter is assumed to be UHINER=
References 1. T. Murayama & Y.Taniguchi, A p J 503,L115 (1998). 2. G.J. Ferland, Hazy: A Brief Introduction t o Cloudy (1998). 3. T. Nagao, T. Murayama & Y.Taniguchi, PASJ 53,629 (2001). 4. T. Nagao et al., A J 125, 1729 (2003). 5 . T. Nagao, T. Murayama & Y.Taniguchi, A p J 549,155 (2001).
PROFILE VARIABILITY OF THE H a AND HP BROAD EMISSION LINES IN NGC 5548*
A.I. SHAPOVALOVA~,V.T. DOROSHENKO~,N.G. BOCHKAREV~, A.N. BURENKOVl, L. CARRASC03, V.H. CHAVUSHYAN3, S. COLLIN4, J.R. VALDES3, N.BORISOV1, A.-M. DUMONT4, V.V. VLASUYKl, I. CHILLINGARIAN~,I.S. FIOKTISTOVA~,O.M. MARTINEZ~ Special Astrophysical Observatory of the Russian A S , Nizhnij Arkhyz, Karachaevo-Cherkesia, 3691 67, Russia Sternberg Astronomical Institute, University of Moscow, Uniuersitetskzj Prospect 13, Moscow 119899, Russia Instituto Nacaonal de Astrofisica, Optica y Electrdnica, INAOE, Apartado Postal 51 y 216, 7200, Puebla, Pue., Mdxico
LUTH, Observatoire de Paris, Section de Meudon, Place Janssen, 92195, Meudon France Benemdrita Universidad Autdnoma d e Puebla, Facultad de Ciencias Fisico-Matema'ticas, Apdo. Postal 1152, C.P. 72000, Puebla, Pue. Mdxico
Between 1996 and 2002, we have carried out a spectral monitoring program of the Seyfert galaxy NGC 5548 with the SAO (Russia) 6 m and 1 m telescopes and with the 2.1 m telescope of the Guillermo Haro Observatory (GHO) located in Cananea, MBxico. High quality spectra with S/N> 50 in the continuum near H a and HP, covering the spectral range -4000-7500 8, with a 4.5 to 15 A-resolution, were obtained.
1. Summary of our main results We found that both the flux in the lines and the continuum gradually decreased, reaching minimum values during May-June 2002. The maximum 'This work has had financial support from INTAS (grant N96-0328), RFBR (grants N97-02-17625, N00-02-16272 and N03-02-17123), state program Astronomy (Russia), and CONACYT research grants G28586-E, 32106-E, and 39560-F (Mexico).
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amplitude ratios of the flux variations during this period were: for HP 4.7; for H a 3.4; and for the XX5190A continuum 2.5. In the minimum state, the wings of H P and H a became extremely weak, corresponding to a Sy1.8 type, not to a Syl, as observed previously when the nucleus was brighter. The line profiles were decomposed into variable and constant components. The variable broad component is well correlated with the continuum variation. It consists of a double peaked structure with radial velocities f l O O O km/s relative to the narrow component. A constant component, whose presence is independent of the continuum flux variations, shows only narrow emission lines. The mean, rms, and the average over years, observed and difference line profiles of HP and H a reveal the same double peaked structure. The relative intensity of these peaks changes with time. During 1996, the red peak was the brightest, while in 1998 2002, the blue peak became the brighter one. Their radial velocities vary in the (500 - 1200) km/s range. In 2000 - 2002, a new bright bump is clearly seen in the red wing of the broad lines at a radial velocity of about +2500 km/s. We have measured the radial velocity of the peak of this bump using good spectra derived with the same resolution (8-9) and a high S/N ratio 250. We found that the radial velocity of this feature decreased between 2000 and 2002 from +2600 km/s to +2000 km/s. The fluxes of the various parts of the line profiles change in an almost identical manner being highly correlated both with each other (r 0.94 0.98) and with the continuum flux (r 0.88 - 0.97). These facts indicate that the flux variability in different parts of the line profiles on short time scales is caused mainly by the reverberation effect. However shape changes of the different parts of the broad line are not correlated with continuum variations and, apparently, are not related to reverberation effects. Changes of the integral Balmer decrement are, on average, anticorrelated with the continuum flux variations. This is probably due to an increasing role of collisional excitation as the ionizing flux decreases. Our results favor the formation of the broad Balmer lines in a turbulent accretion disc with large and moving “optically thick” inhomogeneities, capable of reprocessing the central source continuum.
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BVRI SURFACE PHOTOMETRY OF THE SEYFERT GALAXY SBS 0748+499
J. TORREALBA, E. BENITEZ AND A. FRANCO-BALDERAS IA-UNAM, Apartado Postal 70-264, Mkxico DF-04510, Mkxico;
[email protected] x We are carrying out the first study of the host galaxy associated to the LLAGN SBS 0748+499. This object is part of a subsample of AGN that was isolated from the Second Byurakan Survey (SBS). We have obtained B,V,R and I total magnitudes and also performed surface photometry calibrated in Landolt's system. From the geometric parameters such as the ellipticity ( E ) , the position angle ( P A ) and the parameter we found that the host galaxy shows evidence of low-brightness spiral-arms and a bar-like structure.
1. Introduction The fueling mechanism in AGN is unknown, so far the aim of this work is to establish the morphology of the host galaxy associated to SyG SBS 0748+499 ( z = 0.024; Falco et al. 1999) to try to explain the activity in this galaxy. We used polygonal aperture photometry to obtain the total apparent magnitudes in BVRI of this object and performed surface photometry to characterize the global structure of the galaxy, also we obtained de ratio B/D that can be associated with morphological type. 2. Results and Conclusions We obtained BVRI aperture photometry for SBS 0748+499 using the 1.5m telescope SPM observatory. Our values are: B=15.55 f 0.04, V=14.58 f 0.01,R=13.96 f 0.02, and I=13.20 f 0.02; inside an elliptical aperture of 14 kpc ( p ~ =25 mag/arcsec2), we estimated L B 2.5 x lo1' L a which is in agreement with the mean value found for SyG in the study of Chatzichristou (1999). We also obtained the surface brightness profiles (see Fig. 1) of the galaxy and made the decomposition profile in the R band until the limit pg= 25 mag/arcsec2 using the iterative method of Kormendy (1977). We obtained re, perr, and po, that yields a value for the ratio B/D= 1.23. Accordingly with Schmidtke et al. (1997) the B/D value corresponds to N
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202 an intermediate type galaxy. In addition, we study the behavior of E , PA and a4 and found evidence for the low-brightness spiral-arms and a bar-like structure. Connecting all these elements along with the observed images we propose that the morphological type for the host galaxy of SBS 0748+499 is S(B)a. A preliminar result based on follow-up observations (low-resolution optical spectroscopy) indicates that this object probably is a Sy 1.9 type AGN. This will be define in a future work with better resolution data.
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Figure 1. (a) Surface Brightness Profile; (b) Decomposition profile; inner cut-off radius of 2”, the bulge’s parameters obtained are the effective radius re=1.l kpc (H0=50 km s-l Mpc-l) and the surface brightness pe= 18.07 mag/arcsec2; for the disk the scale lenght is r,=11.4 kpc and po= 22.02 mag/arcsec2; (c) and(d) Geometric Parameters E and PA respectively vs semi-major axis a; (e) Parameter @/a (dislcy OT boxy); i = 33 O .
References 1. J. Kormendy, ApJ 217,406 (1977). 2. P.C. Schmidtke et al., A J 113,569 (1997). 3. E. Chatzichristou, Ph. D Thesis, Leiden University, The Netherlands (1999). 4. E. Falco et al., PASP 111,438 (1999).
Unification and Unconventional AGN
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Marek Kukula and Roberto Maiolino
Paul Martini and Pat Osmer
UNIFICATION OF RADIO-QUIET AGNS: SUCCESSES AND FAILURES
S. VEILLEUX* Department of Astronomy University of Maryland College Park, MD 20742 E-mail: veilleux8astro.umd. edu
This paper reviews the successes and failures of the unification model for radioquiet AGNs, taking into account the recent results from large optical, infrared, and X-ray surveys.
1. Introduction
At the JuIy 2002 Meudon meeting, I wrote a review’ on the AGN paradigm for radio-quiet objects. Since then, more than one hundred papers with “AGN unification” or “AGN unified scheme” in the abstract have appeared under NASA ADS! This flurry of papers has been fueled in large part by extensive new datasets from the 2dF, SDSS, and 2MASS surveys, and the exquisite images and spectra from space missions like HST, ISO, BeppoSAX, CXO, XMM-Newton. It has become clear in the last few years that a thorough test of the AGN unification model is possible only when considering large multiwavelength datasets. In this paper, I discuss the pros and the cons of the unification model for radio-quiet AGNs. The term failures in the title may be too strong and should perhaps be replaced by complications. Although we cannot rule out the possibility that these complications reflect fundamental flaws in the model (e.g., the epicycles of the Ptolemaic model of our Solar System!), I argue below that it seems unlikely that this is the case here. The basic features of the standard unification model are described in 52. The observational evidence in favor of this model is summarized in the next section *This review was presented when the author was on sabbatical at the California Institute of Technology and the observatories of the carnegie Institution of Washington.
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206 ($3), while the main problems with this model are discussed in $4. The contentious issues are summarized in 55. 2. T h e Standard Unification Model
Seyfert 1 QSO 1
Seyfert 2 QSO 2
Figure 1. Standard Unification Model for Radio-Quiet AGNs (based on a sketch of radio-loud AGNs in Urry & Padovani 1995).’
The basic picture is shown in Figure 1 (based on Urry & Padovani 1995).2 The key components are: (1) A central supermassive black hole (SMBH) with mass lo5 - lo9+ Ma. (2) An accretion “disk” on a scale of 5 1 pc, which emits the bulk of the UV and X-rays. (3) An obscuring “torus” which extends on a scale of 100 pc or more and possibly intercepts an important fraction of the ionizing radiation and reprocesses it into the infrared. (4)A broad-line region (BLR) which extends on a scale of 1 - 10 pc. (5) A narrow-line region (NLR) which extends on a scale of 100 pc or more. (6) And finally a wind component which is responsible for the blueshifted narrow or broad absorption line systems detected on sub-pc scale and possibly also the emission-line and X-ray emitting structures seen on kpc scale. In this picture, Type 2 systems (i.e. low-luminosity Seyfert 2s and high-luminosity QSO 2s) are fundamentally the same objects as Type 1 systems except for the fact that they happen to be viewed more edge-on than Type 1 systems and therefore a larger column of dusty and X-ray N
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absorbing material hides the BLR from direct view. 3. Support for the Unification Model
A. H2O Masers. Direct support for this basic picture comes from VLBA observations of spatially resolved sub-pc HzO masers in a few radio-quiet AGNs. NGC 4258 is still arguably the best case for a disk structure surrounding a massive compact ~ b j e c t although ,~ similar structures may also be present in NGC 10684>516>7 and NGC 4945.8 The absence of H2O masers in Seyfert ls9 suggests that the line-of-sight column density in these objects is on average smaller than in Seyfert 2s, as expected in the unification model (see Braatz this conference for a detailed update of this topic). B. Profile of Fe K a . Indirect evidence for an accretion disk is sometimes detected in the X-rays. A very broad (230,000 km s-’), skewed Fe K a line is observed in a few Seyfert Is, suggestive of high velocity material located within a few gravitational radii of the black hole (e.g., MCG-0630-15,1° Mrk 205,11 and Mrk 509l’). Unfortunately, most Fe K a profiles observed with CXO and X M M have FWHM 5 5000 km s-l and are therefore probably produced on a much larger scale (e.g., Ref. 13 and references therein).
C. Ionization Cones. The presence of kpc-scale “ionization cones” in line emission and X-rays is another indirect sign for an axisymmetric disk structure in AGNs. This biconical structure aligns with the radio axis rather than with the minor or major axis of the host galaxy.14i15On average, this structure is more concentrated and circular in Seyfert 1s than in Seyfert 2s,l6>l7as expected in the unified scheme. Recent deep tunable filter imaging of Seyfert galaxies reveals AGN-ionized gas on scales of 10 - 100 kpc.18 The radial and azimuthal dependence of the line ratios measured within these ionization cones provide constraints on the radiation field and the structure of the inner obscuring disk/torus in these objects. N
D. Spectropolarimetry. Arguably the most convincing evidence in favor of the unification model of radio-quiet AGNs comes from spectropolarimetric observations. In his latest paper, Tran (2003)19finds that 50% of local Seyfert 2s have hidden BLRs (HBLRs) in polarized light. But those with HBLRs appear to have systematically higher [01111 X5007/H/?, Lradio/LFIR, and f25/f60 ratios than Seyfert 2s without HBLRs (see also Refs. 20, 21, 22, 23, 24). The ratios of the Seyfert 2s with HBLRs are similar to those of Seyfert 1s. This seems to suggest the existence of two classes of Seyfert 2
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galaxies, the “pure” Seyfert 2s without any BLRs and the Seyfert 2s with hidden BLRs, contrary to the predictions of the unification model. The jury is still out on this issue, however. Lumsden, Alexander, & Hough (2004)25 recently found a higher HBLR detection rate in Comptonthin Seyfert 2s than in Seyfert 2 galaxies as a whole. The HBLR detection rate in their sample appears to be independent of the dust temperature indicator, f25/f60. These results argue against the existence of a population of pure Seyfert 2 galaxies. One should also be aware of possible orientationdependent biases affecting these results since the optical selection criteria often used to build the samples in these studies may favor Type 1s over Type 2s. These selection criteria may also introduce biases in the contribution from starbursts, although the results of Tran (2003) suggest that this bias is not significant. Finally, there appears to be a consensus that the HBLR detection rate increases with increasing [01111 A5007 or hard X-ray l u m i n o s i t i e ~ This . ~ ~luminosity ~ ~ ~ ~ ~ dependence ~ ~ ~ ~ ~ ~ is ~ discussed in more detail in 54C.
E. Spectral Energy Distribution (SED). The UV SEDs of Seyferts are consistent with the unification model. The weaker Big Blue Bump in Seyfert 2s indicates that the obscuration is indeed higher in Type 2s than in Type Is (e.g., Ref. 30 and references therein). I S 0 data suggest that the effects of obscuration are also detectable out to 7 pm. The continuum of Seyfert 2s at this wavelength is weaker than in Seyfert Is, and the equivalent width of the polycyclic aromatic hydrocarbon (PAH) feature in this energy band is stronger in Seyfert 2s, as expected if the extinction is on average A” 90 mags. in these objects.31 N
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F. Obscured BLRs. The sensitivity of the latest generation of nearinfrared spectrographs has allowed systematic ~ e a r ~ forh ob-e scured BLRs in Seyfert 2 galaxies. This technique has revealed BLRs in a number of UV- and infrared-selected Seyfert 2s, including a few objects where the BLR is not visible in polarized light. G . X-ray Absorbing Columns. The near-infrared spectroscopic searches for BLRs described in the previous paragraph can only probe environments with NH 2 5 x lo2’ cmP2 ( ~ 23). ~Hard~ X-ray observations, on the other hand, penetrate down to cm-2 and are therefore a very powerful tool to test the unification model. The results from GINGA, ASCA, and BeppoSAX show that Seyfert 2s generally have larger absorbing columns than Seyfert Is, as expected in the unification But N
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unfortunately, the X-ray data do not constrain the exact geometry and location of the obscuring material in these objects. Absorption by a sub-pc scale disk or torus cannot be distinguished from that by the host galaxy, so it is not possible to use these data alone to test the unification model in detail. This issue is revisited in $4.
H. Broad Absorption Line Quasars (BAL QSOs). Recent submm surveys by Willott et al. (2003)38 and Lewis, Chapman, & Kuncic (2003)39 indicate that BAL QSOs do not have higher submm luminosities than nonBAL QSOs. This is consistent with the unification model where BAL QSOs are the same objects as non-BAL QSOs seen at different viewing angles, and it is inconsistent with the evolutionary model in which BAL QSOs are “young” QSOs in the process of shredding their dusty (star forming) cocoons. 4. Complications to the Unification Model
A. Optical - X-ray Classification Mismatch. Discrepancies between the optical emission-line classification and the classification based on the X-ray spectra fall into three broad categories: 1. Optical broad-line AGNs with significant X-ray a b s ~ r p t i o n2.. X-ray ~ ~ ~bright ~ ~ ~ optically ~ ~ ~ normal ~ ~ (non-active) galaxies ( X B O N G S ) . ~ 3. ~ ?Optical ~ ~ > ~narrow-line ~ AGNs with no obvious X-ray a b s o r p t i ~ n . ~ ~ ~ ~ ~ ~ ~ ~ Inconsistencies between the optical and hard X-rays may be due to a number of factors. E ( B - V ) / N Hof the dust near an AGN may be significantly different from that in our Galaxy. For instance, small grains may not survive in this harsh environment, or the dust-to-gas ratio may be different from its Galactic ~ a l u e . ~ ’ ?Moreover, ~’ the dust is unlikely to be co-spatial with the (neutral and ionized) material that causes the X-ray absorption, so variations in E ( B - V ) / N Hshould not be surprising. XBONGs may be due to inefficient accretion onto the black hole (e.g., ADAF52) or dilution of the AGN signatures by bright galaxy light.53 Finally, hard X-ray spectra of NLAGNs with seemingly modest X-ray absorption often reveal much larger absorbing columns, sometimes close to the Compton thick ~~?~~ limit, when observed with higher S/N ratios or at higher e n e r g i e ~ .An important fraction of the so-called QSO 2s, X-ray detected extremely red objects (EROs) with (R - K) > 5, and ultraluminous infrared galaxies may fall in this last category.
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B. Infrared Spectral Energy Distribution (IR SED). It has been known for some time that the standard compact (51 pc) torus mode156>57i58 has difficulties explaining the broad mid-to-far infrared bump seen in Seyfert galaxies. This bump requires a broad range of dust temperatures (Td 40 - 1000 K) which is not present in the compact torus model. This model also has difficulties explaining the fact that the IR SEDs of Seyferts and QSOs are relatively uniform, while the observed X-ray column densities range from 1021 cm-2 t o cm-2. Finally, these models have difficulties explaining the relatively modest variations in the strength of the 9.7 pm silicate feature among Seyfert galaxies. Several processes may contribute to the observed IR SED. One possibility is that circumnuclear star formation (with relatively cool dust) contributes significantly to the far-IR end of the SEDs.59@0>61 Another possibility is that dust is distributed in a torus or in a warped thin disk which extends much further than 1 pc.62163164965766967 This structure, possibly associated with the host galaxy itself, would allow for a broader range in dust temperatures. This structure may not only contribute t o the IR emisYet sion but also to the obscuration of the central source.68~69~70~71~72~73~74 another possibility is that the torus is clumpy (or fractal?) and has low filling factor. Clumpy torus models75i76>77 have had remarkably good success reproducing the IR SEDs of Seyferts and QSOs and the lack of sensitivity to torus orientation of the SED and silicate feature. N
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C. Luminosity Dependence. The simplest form of the unification model does not predict any luminosity dependence. This is not consistent with observations. The ratio of Type 2 AGNs t o Type 1s decreases significantly with luminosity. Veilleux et al. (1995)78 and Veilleux, Kim, & Sanders 6 for galaxies with infrared luminosities (1999)79 find that this ratio is below 10l1 La, while it is near unity among ultraluminous infrared galaxies. A similar result is found in X-rays, where this ratio ranges from 4 among Seyferts to 0.5 among high-luminosity QSOs (e.g., ref. 80, 81; several presentations a t this conference). The equivalent widths of the UV emission lines82>83and Fe K a lines49l3 are weaker a t high luminosity, and so are the strengths of the UV and X-ray narrow absorption lines.85~86~87@~90 This so-called “Baldwin effect” and the smaller Type 2-to-1 ratios a t high luminosities can both be explained if the covering fraction of the material producing the broad and narrow emission lines and the absorption features decreases with increasing luminosities. One possibility is that the inner radius of the accretion disk or torus recedes with luminosity due to dust sublimation (Ri c( L 1 / 2 ,where L is
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the heating luminosity; e.g., Ref. 91). Another scenario is that the opening angle of the disk/torus/wind structure increases with increasing luminosity (e.g., Ref. 66). These two scenarios may help explain the presence of a very extended (up t o 200 kpc diameter), symmetric, highly ionized nebula in the powerful radio-quiet quasar MR 2251-178.92>18 But a more detailed investigation is necessary to explain the higher detection rate of HBLRs among high-luminosity objects (discussed in $3). The possibility suggested by Laor (2003)93 and Nicastro, Martocchia, & Matt (2003)94of a luminosity or accretion rate threshold to the formation of the BLR does not seem borne out by the data on LLAGNs (e.g., L. Ho a t this conference).
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D. Lack of Obvious Redshift Dependence. The results from the deep CXO and XMM-Newton surveys show no evidence for a strong redshift dependence of a,, = log(f,/fopt)/log(v,/vopt) out t o z 6 (e.g., Ref. 95, 96, 97, 98; although see Ref. 99). There is also no evidence for an obvious redshift dependence of the X-ray power law index, rx (e.g., Hasinger and Barcons, this conierence), and the widths of the recombination lines in BLAGNs (Croom, this conference). These results are quite remarkable given that the properties of the host galaxies (e.g., morphology, gas content) and the environment (e.g., distance to nearest neighbor) are likely to have changed significantly over the age of the universe. It may be that several parameters are indeed changing over this period of time, but the effects more or less cancel each other within the (large) uncertainties of the current measurements. One quantity, however, is clearly changing with redshift: the number density of AGNs. The space density of Seyfert galaxies appears to peak near z 0.7, much later than for the high-luminosity QSOs ( z 2; Ref. 100,101; Hasinger this conference). If confirmed, less luminous (but longer) events may dominate SMBH formation. Differences in the fueling/triggering processes of these events may be at the origin of this strong luminosity dependence. Seyfert galaxies require accretion rates 5 0.1 M a yr-l, while QSOs require 1 - 100 M a yr-l (assuming a constant radiative efficiency of 10% in rest mass units). Local processes (e.g., nuclear bars, spiral arms, ...) are sufficient to fuel a Seyfert galaxy, but galaxy-scale phenomena are probably required to trigger a &SO. Observations in support of merger-induced QSO activity are accumulating for objects a t low redshifts where detailed morphological analyses of the hosts are possible,102~103~104 but it quickly becomes technically challenging t o reach the surface brightness limits required to carry out the same analysis a t redshifts beyond 0.5. N
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5 . Summary and Unanswered Questions
There is strong observational support for the unification scheme, but this scheme must be refined to take into account a number of complications: 1. Not all Seyfert 2s show hidden BLRs. This may be due to either a lack of “mirrors” or a genuine lack of BLRs in these objects. It may be that there are two types of Seyfert 2s, one type where the Seyfert 2 is basically a Seyfert 1 seen at an angle where the BLR is not visible in direct light, and a second type of Seyfert 2 which does not have a BLR at all. Another possible explanation is that the current BLR searches lack the sensitivity to probe Compton-thick Seyfert 2s.
2. Mismatch in the optical and X-ray classifications. AGNs detected in the X-rays are not always detected in the optical. The amount of X-ray absorption is often inconsistent with the inferred extinction at optical or infrared wavelengths. There are several possible reasons for these discrepancies: The dust near the AGN may have non-Galactic E ( B- V ) / N H .The X-ray absorbing material is probably not co-spatial with the dust, so the optical and X-ray measurements probe different environments. The light from the host may also make it hard to detect the AGN optically. ADAF systems are easier to detect in the X-rays than in the optical. Compton thick Seyfert 2s may appear Compton thin in X-ray spectra with modest S/N. 3. Infrared Spectral Energy Distribution. The exact shape of the IR SED and strength of the silicate absorption feature at 9.7 pm cannot be reproduced with a standard (compact) torus model. IR emission from a starburst, emission and extinction from galactic-scale dust or an extended torus, disk or wind, or a compact clumpy torus need to be taken into account to explain the observed IR SEDs.
4. Luminosity Dependence. The ratio of Type 2 to Type 1 objects shows a strong dependence with luminosity. This is seen optically and in the Xrays. The equivalent widths of the UV and X-ray emission and absorption lines decrease with increasing luminosities. The detection rate of hidden BLRs also appears to depend on luminosity. Most of these trends can be explained in the context of the unified scheme if the inner radius of the torus recedes at high luminosities or if the opening angle of the disk, torus, or wind structure is larger in quasars than in Seyfert galaxies.
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5. Evolutionary Effects. Based on the latest data from CXO and XMMNewton, the fundamental structure of the AGN engine does not seem t o
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change with redshift. There is remarkably little evidence for evolution of 6, despite changes in the environment and the the QSO engine out t o z properties of the host galaxy. However, the latest CXO and XMM-Newton deep surveys show that the Seyfert population peaks around z 0.7, while the QSO population peak much later ( z 2). This is likely due t o the fact that QSOs and Seyferts require different accretion rates: the evolution of QSOs may be regulated by major galaxy mergers, while Seyferts are fueled by local processes.
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Acknowledgments The author acknowledges partial support of his research through NSF/CAREER grant AST-9874973 and NASA/LTSA grant NAG 56547. The author also wishes t o thank both the California Institute of Technology and the Observatories of the Carnegie Institution of Washington for their hospitality during his sabbatical.
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Jane Turner
INAOE and UNAM students
NEW INSIGHTS ON UNIFICATION OF RADIO-LOUD AGN
M. CHIABERGE Istituto d i Radioastronomia - C N R via P. Gobetti 101 401.29 Bologna, Italy E-mail: chiab8ira. cnr.it
The radio-loud AGN unification model associates powerful radio galaxies with radio-loud quasars and blazars. In analogy with the radio-quiet scheme, the nuclear regions of objects showing only narrow emission lines in their optical spectrum are thought to be obscured to our line-of-sight by a geometrically and optically thick dusty "torus". In objects showing broad emission lines we directly observe the innermost parsecs around the central black hole, i.e. the broad line region and the accretion disk. Radiation from the base of the relativistic jet dominates the overall emission of blazars, that are seen almost pole-on. Although the broad picture seems to be well established, there are several fundamental aspects that are still to be understood. HST studies have recently shed new light on many issues, from the properties of the nuclei to the structure of the host galaxies.
1. The standard unification picture The standard picture for unification of both radio-quiet and radio-loud
AGN is based on the anisotropy of the nuclear emission: objects intrinsically identical appear different to observers located along different viewing directions. In addition to the presence of 1-to-100pc-scale absorbing tori, radio-loud AGN have two powerful relativistic jets, which constitute a further source of anisotropy. The jets emerge from the innermost regions, and propagate along the rotation axis of the accretion disk formed around the central black The torus blocks the direct view of both the accretion disk and the surrounding broad line region (BLR) to observers located perpendicularly to the jet axis. The extended (kpc-scale) narrow emission line region (NLR) is visible to such an observer, which would classify that object as a narrow-line radio galaxy (NLRG). If the line-of-sight forms a very small angle to the jet axis, the emission is dominated by non-thermal 217
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radiation from the jet, which is strongly boosted by relativistic effectsa. In that case, such object would appear to us as a blazar, i.e. either a flat spectrum radio quasar (FSRQ) or a BL Lac, depending on whether strong emission lines (EW > 5 fr) are present or absent, respectively. For intermediate viewing angles (0 > l/r‘),where the jet radiation appears less boosted or even de-boosted, both the accretion disk and the BLR become visible, and the object appears to us as a steep spectrum radio quasar (SSRQ) or, for lower nuclear luminosities, a broad line radio galaxy (BLRG). Among the various observations that can be performed to prove the validity of such a unification scenario, the detection of a hidden BLR seen through scattered radiation is considered as one of the most solid and direct tests2B1. In fact, scattering mirrors provide a “periscope” for viewing the nucleus from other directions
1.1. Open problems The “zeroth-order’’ unification scheme described above generally accounts for the observational properties of radio-loud AGN. However, several crucial issues are still open, and need further investigation. First of all, there is clear evidence that such a scheme must be split into two different models, in order to account for unification of low and high power objects separately. At high luminosity, radio galaxies with “edge-brightened” (FR 11) morphology are unified with quasars (SSRQ and FSRQ), while for lower powers, radio galaxies with “edge-darkened” morphology (FR I) are believed to be the parent population of BL Lac objects. The need for two different schemes comes from the “absence” of strong emission lines in both BL Lacs and FR I, while strong, high excitation lines are a common characteristic of powerful FR I1 and quasars. Furthermore, in the low-power scheme, the “intermediate” class analogous to BLRG and SSRQ appears to be missing, since only very few examples of broad-lined FR Is are known (see section 5 ) . Thus, the nuclear structure of low and high power objects may differ in some crucial aspect. Let me now summarize what are, in my opinion, the most important open problems. i) The lack of significant broad emission lines in F R I and BL Lacs implies that, in the framework of the unification model, there is no need for the presence of obscuring t o r i in these sources. However, molecular aThe observed integrated flux is enhanced by a factor h4, 6 = [r(l- pc0s6’)]-~ is the beaming factor, B is viewing angle to the jet axis, and r and p are the bulk Lorentz factor and velocity of the jet, respectively.
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tori are thought to be present in all other AGN, and they are also believed to function as a fuel reservoir for the active nucleus; ii) environment: FR Is and BL Lacs seem to prefer different environments. FR I are predominantly found in high density clusters45,while BL Lacs seem to avoid rich clusters30; iii) a few BL Lacs show faint (and variable) broad lined5; iv) a fraction of the BL Lac population shows a radio morphology more typical of FR ]Iz6; v) a substantial fraction of narrow-lined FR I1 have atypical low-ionization optical spectra (L[or11]< L I O I I ~ similar ) to those of FR I, while quasars have L [ O I I I> ~ L [ O I I ]vi) ; although polarized broad emission lines have been observed in a few NLRG (e.g. 3C 234), it is still unclear what is the incidence of such a phenomenon among radio-loud AGN. Furthermore, in many objects the origin for polarization is not clear: scattering and dichroic extinction are two possible interpretation^'^; vii) the quasar fraction in complete samples of radio galaxies is strongly dependent on luminosity43, but it is unclear whether this happens because the inner radius of the torus increases for increasing luminosity of the central quasar, or because of the rise of a distinct population of “starved” quasars at low luminosities. These “phenomenological” issues translate into more general questions on the physical properties of radio-loud AGN: are FR I and FR I1 (or BL Lacs and quasars) physically different? Are their central BH masses different? What are the properties of accretion around the BH? Are their jets different? Do all RL AGN have a BLR? In the following I will try to summarize the current observational scenario.
2. Jets in radio galaxies and quasars
Relativistic jets are seen emerging from the very innermost regions of the active nucleus, on sub-pc scale^^^^^^. Radio observations show that jets are relativistic in both FR I and FR I1 radiogalaxies on parsec scales. Superluminal motions of radio components are observed in a large number of quasars and, although less prominently, also in BL Lacs. In low power radio galaxies, while proper motions of radio components are commonly observed on small scales, the jet slows down to sub-relativistic velocities over distances of 1 - 10 k p ~ Superluminal ~ ~ . motions of optical components have also been observed with the HST in M 87, having apparent speed in the range 4 - 6c thus strongly supporting unification with BL Lacs5. Recently, significant step forward in our knowledge of the structure of jets has been taken. In particular, high resolution radio data have shown the presence of transverse structures in jets associated with both low and
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high power radio galaxies, and even on the VLBI scale2I. Their “limbbrightened” appearance is currently explained as due to the presence of velocity structures in the jet: a fast, highly relativistic “spine” (I’ 15) and a slower external layer which moves at a slower speed, possibly because of the interaction with the surrounding ambient medium. In F R I1 such structures appear to persist on very large scales (>> lokpc, e.g. 3C 35334), indicating that at least the “spine” of F R I1 jets does not suffer substantial deceleration. Independent evidence for large-scale high-speed jets in quasars and FR I1 is provided by X-ray Chandra observations. X-ray emission from large-scale extragalactic jets is best interpreted as a result of inverse Compton emission from relativistic particles scattering off seed photons of the cosmic microwave background3698.Such model requires the bulk Lorentz factor of the jet (spine) to be 15. N
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3. Host galaxies
A fundamental prescription of the unification models is that unified classes must share the same properties as far as the extended (unbeamed) characteristics are concerned. Therefore, the properties of the host galaxy are crucial parameters for testing unification scenarios. Quasar hosts spanning a range of redshift z = 0.1-2 have been extensively studied with the HST16. Radio loud QSO are hosted by bright ( L > L*) massive ellipticals, which are similar in magnitude and morphology to radio galaxies hosts. The same result holds for BL Lacs host galaxies, which appears to be similar to FR I hosts, in substantial agreement with the unification ~ c e n a r i o ~However, ~t~~. the absence of BL Lacs in rich cluster environment^^^ and the lack of dust lanes in BL Lac hosts, compared with those of FR Is in which dust lanes are ubiquitous, are still issues to be addressed. 4. Black hole masses
The correlations between the mass of the central black hole and some fundamental parameters of the host galaxy (either the central stellar velocity dispersion o or the optical magnitude of the bulge Lbulge)37729 are considered as powerful tools to estimate MBHwithin an accuracy of a factor 2-3. But the determination of the velocity dispersion and/or the optical magnitude of the host is not always straightforward, especially if a strong nuclear component is present, such as in the case of quasars and BL Lacs. BH masses of BL Lacs have been estimated by3917 using the MBH- o relation, obtaining values in the range 5 x lo7 - 1 x 109M,. The distributions of
22 1
central BH masses in BL Lacs and radio galaxies (of all species) appear to be consistent, thus supporting unification. However, to the best of my knowledge, a detailed comparison of well defined and statistically complete samples has not been performed yet. Concerning high power objects, the BH mass of a sample of radio loud QSO and radio galaxies has been estimated using HST images of their host galaxies and the MBH - &lge relation2g. These objects share a common range in MBH but, interestingly, it appears that radio loud AGN have BH masses confined to MBH > 10gMa. However, other authors do not find any relationship between radio-loudness and central black hole mass44. 5 . The HST view of FR I and FR I1 nuclei: implications for unification
Figure 1. Left: the central 6 arcsec of 3C 449 as seen with HST/WFPCB. Right: optical CCC luminosity versus radio core luminosity for 3CR FR Is.
FR I: Optical nuclear studies of radio galaxies provide us with crucial information on the physical processes at work in their central regions. Furthermore, a direct test of the unification scheme, based on the nuclear emission, can be performed. HST has allowed us to study faint unresolved sources that are present in the center of most FR Is from the 3CR catalogg (but see also other ~ o r k s ~ ?We ~~ found ) . that these Central Compact Cores (CCC) show a tight correlation with the radio core emission (both in flux and luminosity) which strongly argues for a common synchrotron origin from both components (Fig. 1). The detection of CCCs in 85% of the complete sample indicates that we have a direct view of the innermost nuclear regions in the vast majority of FR I. Thus it appears that a “standard” geometrically
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and optically thick torus is not present in low luminosity radio galaxies. Any absorbing material must be distributed in a geometrically thin structure (thickness over radius ratio 5 0.15) or, alternatively, thick tori are present only in a minority of FR I. The CCC fluxes are upper limits to any thermal disk emission. This implies extremely low radiative efficiency for the accretion process. The observed CCC emission corresponds to 5 lo-’of the Eddington luminosity for a 1 0 8 M ~ black hole, which appears to be typical for these radio galaxies. This might also explain the lack of strong photo-ionized emission lines in the optical spectra of both FR Is and BL Lacs. The picture which emerges is that the innermost structure of FR I radio galaxies (and thus also of BL Lacs) differs in many crucial aspects from that of the other classes of AGN; they lack the substantial BLR, tori and thermal disk emission, which are instead associated with all other active nuclei. A fine test for such a scenario has been obtained in the case of M 87, a famous and relatively powerful FR I radio g a l a ~ y ~M~ 87 ? ~was ~ .observed in the infrared at lOpm with the Keck and Gemini telescope, and no significant mid-IR nuclear excess is found. This supports the absence of a hidden quasar-like accretion process in the nucleus, which would heat the surrounding obscuring dust, thus producing a strong thermal IR excess, when compared to the optical observed flux. Of course it would be very interesting to extend this analysis to complete samples. In two cases (Centaurus A and NGC 6251) the nuclear spectral energy distribution (SED) has been derived from the radio to the gamma-ray band. The SEDs show two broad peaks, very similar to those observed in BL Lacs and usually interpreted as non-thermal synchrotron and inverse Compton emission22. The SED has been modeled in the framework of synchrotron self-Compton e m i ~ s i o nobtaining ~ ~ ~ ~ physical ~ ~ ~ ~parameters , for the source that are completely in agreement with those of BL Lacs of similar total power, thus quantitatively supporting the unification scenario. Furthermore, we found evidence that the emitting region in FR I has a slower bulk Lorentz factor (I’ 2), when compared to BL Lacs. This can be interpreted as a signature of the presence of velocity structures in the jet, e.g. a fast spine and a slower (but still relativistic!) layer similar to those observed in radio VLBI images. The spine dominates the emission in BL Lacs, while the slower layer is visible only when the jet direction forms a large angle to the observer’s line-of-sight. But are all FR I “starved quasars”? In fact, very few “broad-lined” FR Is, showing the signature of radiative efficient accretion and substantial N
223 BLR, are known. A famous example is 3C 120, which is associated to a peculiar SO galaxy35. A few other FR I quasars have been recently found in deep radio samples6. However it is still unclear whether they represent a substantial fraction of the entire FR I population that have been “hidden” by a selection bias, or they are only rare peculiar sources.
FR 11: On average, FR I1 host galaxies are less luminous with respect to those of FR Is28 (but this is probably only because of selection effects40) and belong to lower density groups, at least at low red shift^^^. One of the major unsolved issues for unification is the role played by a sub-class of lowionization FR I1 (LEG). Such objects have an FR I1 radio morphology, but their optical spectral properties are similar to those of FR I. Our analysis of HST images of the nuclei of 3CR FR IIl0 up to z = 0.3 led us to intriguing conclusions. The first surprising result is that, as in the case of FR I, most of the galaxies show central unresolved components, regardless of their optical spectral classification. In the framework of the AGN unification scheme we would not expect to observe such optical nuclei in objects that do not show broad lines in their optical spectrum. In fact, their central regions should be hidden by the presence of thick obscuring tori. Broad-lined objects (quasars and broad line radio galaxies, BLO) have the brightest nuclei, which show a large optical excess with respect to the radio-optical correlation found for FR I (Fig. 2a). This is readily explained if the dominant component in the optical band is due to thermal emission from an accretion disk. Indeed, these nuclei appear to have flatter optical-to-UV spectral index (Q,-UV 5 1) when compared to that of “synchrotron” FR I nuclei, and similar to that of other radio-loud QSOl1. We also found that optical erg s-’ Hz-l. This might be nuclei of BLO are present only for Lo > the manifestation of a threshold in the efficiency of the accretion process, from the standard optically thick, geometrically thin accretion disk to low radiative accretion flows. The nature of the nuclei of the High Excitation Galaxies (HEG) is certainly more complex, since some of their nuclei may be compact scattering regions which fall on the F R I correlation “by chance”. In order to discriminate between scattered nuclei and nuclei seen directly, we should refer to an isotropic parameter. The luminosity of the [OIII] emission line is believed to be a good indicator of the strength of the nuclear ionizing continuum. In Fig. 2b we show that sources separate in the plane formed by the ‘‘nuclear” EW of the [OIII] line vs the optical excess with respect to the non-thermal jet emission. BLO, LEG and FR I have low EW values (- 102.5A) and they only differ by the amount of optical excess. On the other hand, all but
224 8
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Figure 2. Left: (a) optical CCC vs. radio core luminosity for 3CR FR I and FR I1 with z < 0.3. The dashed line is the FR I correlation Right: (b) Nuclear EW of the [OIII] emission line vs. the logarithm of the ratio between optical and radio core luminosity. The dashed lines separates scattered nuclei from nuclei seen directly.
two of the HEG have much larger equivalent widths ( 2 103.5A). This is indeed expected from the unified models, as obscuration reduces the observed nuclear continuum, while the line emission is less affected or unaffected. A strong ionization source, obscured to our line-of-sight, must be present in sources with a very high value of EW[OIII]. We argue that all sources with high EW are hidden quasars, and their nuclei are seen through scattered radiation, while the low EW region of the diagnostic plane includes the objects in which we directly see the source of ionization. It is important to note that most of the LEG lie among the FR I in both diagnostic planes. Therefore, from the point of view of their radiooptical nuclear properties, these objects are indistinguishable from FR I. This picture leads t o a new dichotomy for radio galaxies, which is not based on their radio morphology but on their nuclear properties. The LEGs should be considered as part of the same group as the FR I. A direct implication for the unifying scheme is that, when observed along the jet axis, LEGs should appear as BL Lac objects. Therefore, LEGs may be identified as the parent population of those BL Lacs with extended radio morphology26. Interestingly, both the evolution and unification of FR I and FR I1 with BL Lacs and flat-spectrum quasars (FSRQ) can be explained by a dual-population scheme24,which considers FR Is and LEGs as a single population, associated with BL Lacs, while all other FR I1 are unified to quasars. And our HST results basically confirm such a scenario.
225 6. Is there any radio-loud AGN sequence?
The properties of the SED of blazars are well described by a single parameter, namely the bolometric luminosity18. As luminosity decreases, the frequency of the synchrotron peak increases as well as the ratio between the luminosity of the Synchrotron to inverse Compton peak. This characterizes the “blazars sequence”, from FSRQ to low-energy-peaked BL Lacs (LBL) to high-energy-peaked BL Lacs (HBL), which have the synchrotron peak in the X-rays. Such a trend appears to be strictly connected with the intensity of the radiation field surrounding the relativistic jet22: the position of the peaks of the SED is determined by the break of the emitting particles energy distribution, which is located at a lower energy for higher intensity radiation fields. This theoretical scenario implicitly predicts that high-energy-peaked blazars with strong emission lines (HFSRQ) should not exist. Recently, a population of HFSRQ might have been identified3I. However, although their peak energy appears to be higher than that of “classic” FSRQ, Vpeak values are not as extreme as those of HBLs. This means that there may be a physical limit in Vpeak for sources with a strong radiation field surrounding the jet. Can we translate such a scenario into a physical sequence for radio galaxies? It is tempting to speculate on the existence of a similar sequence starting from low-power FR Is through HEGs (and BLRGs), with the LEGS acting as an intermediate class. But it is unclear if the differences between the various classes of RG are driven by e.g. a change in the physical conditions of the accretion process, which may also affect the properties of emission line fieldlg. I believe this is one of the most interesting aspects of the unifying scheme for radio loud AGN to be investigated in years to come.
Acknowledgments
I apologize for the many omissions of my talk: the topic is immense, and it is impossible to be complete. Most of the work on radio galaxies’ nuclei summarized here have been done with the fundamental contribution of other people. I wish to thank in particular Alessandro Capetti, Annalisa Celotti and Duccio Macchetto for productive collaboration and constant support. Finally, I wish to congratulate the LOC and the SOC, and in particular Raul and Roberto, for organizing a very successful meeting in such a beautiful place. References 1. R. Antonucci & R. Barvainis, ApJ 363, L17 (1990).
226 R.R.J. Antonucci & J.S. Miller, ApJ 297,621 (1985). A.J. Barth, L.C. Ho & W.L.W. Sargent, ApJ 583,134 (2003). P.D. Barthel, A p J 336,606 (1989). J.A. Biretta, W.B. Sparks & F. Macchetto, ApJ 520,621 (1999). K.M. Blundell & S. Rawlings, ApJ 562,L5 (2001). A. Capetti et al., A&A 383,104 (2002). 8. Celotti, A., Ghisellini, G., & Chiaberge, M. 2001, M . N . R . A . S . , 321,L1 9. Chiaberge, M., Capetti, A., & Celotti, A. 1999, A&A, 349,77 10. Chiaberge, M., Capetti, A., & Celotti, A. 2002, A&A, 394,791 11. Chiaberge, M., Macchetto, F. D., Sparks, W. B., et al. 2002, ApJ, 571,247 12. Chiaberge, M., Gilli, R., Capetti, A. et al. 2003, ApJ, 597,166 13. Chiaberge, M., Capetti, A., & Celotti, A. 2001, M . N . R . A . S . , 324,L33 14. Cohen, M. H., Ogle, P. M., Tran, H. D. et al. 1999, A J , 118,1963 15. Corbett, E. A,, Robinson, A., Axon, D. J., et al. 1996,M.N.R.A.S., 281,737 16. Dunlop, J. S. et al. 2003, M . N . R . A . S . , 340,1095 17. Falomo, R., Kotilainen, J. K., & Treves, A. 2002, ApJ, 569,L35 18. Fossati, G., Maraschi, L., Celotti, A. et al. 1998, M . N . R . A . S . , 299,433 19. Ghisellini, G. & Celotti, A. 2001, A&A, 379,L1 20. Giovannini, G., Cotton, W. D., Feretti et al. 2001, ApJ, 552,508 21. Giovannini, G., Taylor, G. B., Arbizzani, E. et al. 1999, A p J , 522,101 22. Ghisellini, G., Celotti, A., Fossati, G. et al. 1998,M.N.R.A.S., 301,451 23. Guainazzi, M., Grandi, P., Comastri, A. et al. 2003, A B A , 410,131 24. Jackson, C. A. & Wall, J. V. 1999, M . N . R . A . S . , 304,160 25. Junor, W., Biretta, J . A., & Livio, M. 1999, Nature, 401,891 26. Kollgaard, R. I . , Wardle, J. F. C., Roberts, D. H. et al. 1992, A J , 104,1687 27. Laing, R. A., Parma, P., de Ruiter, H. R. et al. 1999, M . N . R . A . S . , 306,513 28. Ledlow, M. J. & Owen, F. N. 1996,AJ, 112,9 29. McLure, R. J. & Dunlop, J. S. 2002, M . N . R . A . S . , 331,795 30. Owen, F. N., Ledlow, M. J., & Keel, W. C. 1996, A J , 111,53 31. Padovani, P., Perlman, E. S., Landt, H. et al. 2003, ApJ, 588,128 32. Perlman, E. S., Sparks, W. B., Radomski, J. et al. 2001, ApJ, 561,L51 33. Scarpa, R., Urry, C. M., Falomo, R. et al. 2000, ApJ, 532,740 34. Swain, M. R., Bridle, A. H., & Baum, S. A. 1998, ApJ, 507,L29 35. Tadhunter, C. N. et al. 1993, M . N . R . A . S . , 263,999 36. Tavecchio, F., Maraschi, L., Sambruna, R. M. et al. 2000, A p J , 544,L23 37. Tremaine, S., et al. 2002,ApJ, 574,740 38. Urry, C. M. & Padovani, P. 1995, P A S P ,107,803 39. Urry, C. M., Scarpa, R., O'Dowd, M. et al. 2000, A p J , 532,816 40. Scarpa, R. & Urry, C. M. 2001, A p J , 556,749 41. Verdoes Kleijn, G. A. et al. 2002, A J , 123,1334 42. Whysong, D. & Antonucci, R. 2004, ApJ, 602,116 43. Willott, C. J. et al. 2000, M . N . R . A . S . , 316,449 44. Woo, J . & Urry, C. M. 2002, ApJ, 581,L5 45. Zirbel, E. L. 1997, ApJ, 476,489
2. 3. 4. 5. 6. 7.
GBT MONITORING AND SURVEYS FOR H20 MASER EMISSION IN AGNS
J. A. BRAATZ National Radio Astronomy Obseruatory PO Box 2, Green Bank, WV 24944, USA E-mail:
[email protected] C. HENKEL Max-Planck-Institut fur Radioastronomie Auf dem Hugel 69, 0-53121, Bonn, Germany L. J. GREENHILL AND J. M. MORAN Haruard-Smithsonian Center for Astrophysics 60 Garden St., Cambridge, M A 02138, USA A. S. WILSON Department of Astronomy, University of Maryland College Park, MD 20742, USA
We are using the Green Bank Telescope (GBT) to study the nuclear gas in active galaxies through observations of the 22 GHz water maser line. We have been monitoring multiple sources over 1.7 years and have confirmed and refined previous measurements of velocity drifts in both IC 2560' and Mrk 1419'. In NGC 1386 the velocity drifts in all maser components are small, < 0.5 km s-l yr-'. We are also revisiting surveys for water maser systems in nearby (v < 12000 km/s) type 2 AGNs. Several new sources have been discovered, including masers in the nuclei of NGC 6323, NGC 5728, and NGC 4388. Each of these has maser components at large velocity offsets (up t o 550 km/s) from the systemic velocity, suggesting the presence of a nuclear disk. In NGC 6323 and NGC 4388, maser components are detected near the systemic velocity as well. Our results confirm that water vapor emission in AGNs is more common than previously shown.
1. Introduction
Powerful water maser emission at 22 GHz has been detected in about 40 extragalactic sources, all of them AGNs. In certain maser systems there 227
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is evidence that the molecular gas exists in a pc-scale disk centered on the dynamical center of the AGN. When present, nuclear masers provide the only means of directly mapping the morphology of gas at such small distances from the central engine. The prototype disk maser is in NGC 4258. Its spectral profile shows three clusters of maser components that originate at distinct loci: one cluster near the systemic velocity of the galaxy forms on the near side of the inclined nuclear disk, and clusters red- and blue-shifted by 900 km s-l originate at the projected edges of the disk and are shifted according to the rotation velocity. The maser in NGC 4258 allows one to measure the gravitational acceleration, rotation velocity, and linear size of the molecular disk with high precision; hence the black hole mass and even the distance to the nucleus is determined3q4. Surveys for new H2O maser systems have yielded low detection rates, typically < 5%, but are strongly limited by sensitivity. The Green Bank Telescope (GBT) provides significant improvements in sensitivity and bandwidth coverage over the previous generation of telescopes working at Kband. The bandwidth is significant because in a given maser system, the high velocity masers are often the brightest. We are using the GBT to revisit a survey of nearby type 2 AGNs. We are also pursuing monitoring studies of H2O systems in order to track possible velocity drifts in individual maser features. Maser drifts can be used to measure the centripetal force on the gaseous disk, and are complementary to VLBI observations used to characterize the dynamics in the disk.5
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2. Results
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Among 145 galaxies searched with the GBT so far, our survey has revealed 10 new masers, adding 25% to the list of known extragalactic H2O sources. Each of these galaxies has been observed and undetected in previous surveys. Figure 1 shows spectra of three of the newly discovered masers. Each has high velocity components that suggest disk structure. The maser in NGC 6323, in particular, has a classic triple-peaked spectrum with an inferred disk rotation velocity of 550 km s-'. The maser in NGC 5728 has a rich spectrum of high velocity components with a rotation velocity up to 250 km s-l, but no systemic components are apparent in its spectrum. In NGC 4388 the masers are fainter, but reveal a probable disk rotating at 400 km s-'. Complete results of the survey are being prepared for a later publication. One can also find results of ongoing surveys at
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229 http://www.nrao.edu/Nj braatz. I
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Figure 1. The spectra of three HzO masers discovered during surveys in nearby type 2 AGNs. Each spectrum shows 1400 km s-' coverage. The cross mark above each spectrum shows the systemic velocity of the galaxy, with the horizontal line in the cross showing the uncertainty. The spectra of NGC 4388 and NGC 5728 were taken on March 7, 2003 and the spectrum of NGC 6323 was taken on June 2, 2003.
Masers in several galaxies are also being monitored with the GBT. We confirm the detection of velocity drifts in the systemic maser features in Mrk141g2. We also confirm the detection of a velocity drift in IC 25601 and find no velocity drift > 0.5 km s-l yr-l in either the systemic or high velocity features of NGC 1386 (Figure 2). Braatz et al. (2003) discuss the implications of such measurements. Our data on IC 2560 include evidence that maser features are drifting at various rates. In particular, the two strongest features near 2910 km s-l in the April 2002 spectrum of IC 2560 drift at 1.3 f 0.7 km s-l yr-' and 4.5 f 0.7 km s-l yr-'. If confirmed, the data suggest that the systemic maser features are formed in gas at a variety of radial distances from the central black hole. This result requires confirmation that will come with additional epochs of data.
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Figure 2. Example maser spectra of NGC 1386 (top) and IC 2560 (bottom) taken over 1.7 years with the GBT. The April 2002 data have a channel spacing of 1.3 km s-l while all others have a channel spacing of 0.3 km s-'. Spectra from different epochs are plotted with a vertical offset for clarity.
References 1. Y . Ishihara, N. Nakai, N. Iyomoto, K. Makishima, P.J. Diamond & P. Hall, P A S J 5 3 , 215 (2001). 2. C. Henkel, J.A. Braatz, L.J. Greenhill & A.S. Wilson, A&A 394, 23 (2002). 3. M. Miyoshi, J. Moran, J. Herrnstein, L. Greenhill, N. Nakai, P. Diamond & M. Inoue, Nature 373, 127 (1996). 4. J.R. Herrnstein, J.M. Moran, L.J. Greenhill, P.J. Diamond, M. Inoue, N. Nakai, M. Miyoshi, C. Henkel & A. Riess, Nature 400, 539 (1999). 5. J.A. Braatz, A.S. Wilson, C. Henkel, R. Gough & M. Sinclair, A p J S 146,249 (2003).
OBSCURED AGN AND TYPE I1 QSOS IN CHANDRA CLUSTER FIELDS
P. GANDHI European Southern Observatory, Casilla 19001, Santiago, Chile E-mail:
[email protected] M . A. WORSLEY, C. S. CRAWFORD AND A. C. FABIAN
Institute of Astronomy, Huntingdon Road, Cambridge CB3 OHA, England
We present results on the first, wide-area study to concentrate on the properties of distant, powerful, X-ray selected, obscured AGN discovered serendipitously in 10-70 ks Chandra observations. We are able to study in detail three luminous type 2 quasars with LxPray> erg s-l & obscuring column density > loz3 cm-2; and identify more good examples of such sources, enabling us to derive a lower limit 0 The possibility of the existence to the space density of Q S 0 2 s to be ~ 1 deg-'. of completely obscured AGN (47r covering fraction with little or no scattered light into the line-of-sight) is discussed through the example of a high resolution VLT spectrum of one such Seyfert 2 identified in our sample.
1. Introduction
Two of the most intriguing results to emerge from recent X-ray surveys by Chandra and XMM-Newton are: i) the discovery of a large number of AGN with little evidence of activity in the optical/near-infrared; and, ii) the surprisingly low-redshift ( z 0.7) peak in their space distribution. While the former observation implies that many AGN are either completely enshrouded with dust or powered by non-efficient accretion processes, the latter reveals a resurgence in Universal accretion activity after the epoch associated with optical quasars ( z 2). The latter also implies that the typical sources powering the X-ray background (XRB) are not type 2 quasars, as assumed by early synthesis models', but lower-luminosity Seyfert 2s. It is then pertinent to ask whether there exists a large population of type 2 QSOs. If they really are the high-luminosity counterparts of Seyfert 2s, why are they not found in numbers comparable to optically-selected (unobN
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scured) quasars? QS02s are also thought to be the hidden sites of growth of the most massive black holes, and are likely to be absorbing and reprocessing a large fraction of AGN light into the mid- to far-infrared. 2. A sample of powerful, obscured AGN
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Type 2 QSOs
Our sample' was selected from the fields of Chandra observations of galaxy clusters and radio galaxies, which were the main target of the observations. The 12 fields chosen for analysis, covering 1 deg2, are listed in Table 1. Serendipitous point X-ray sources were detected all over the ACIS-S field of view, and the harder, optically-faint sources (absent or a t least very faint on the DSS) were followed up with J H K imaging a t the United Kingdom InfraRed Telescope. It was found that most X-ray sources with fluxes F0.5-7keV 2 5 x l o w 5 erg s-l cmP2 were easily detected in the K-band down to K=20. N
Table 1. The Chandra fields analysed. The last column gives the number of hard sources detected, and, in brackets, their percentage relative to the total sample in each field. Field [Obs Id] Perseus l8000101 RXJ 0820.9+0752 B2 0902+343 IRAS 09104+4109 Abell 963 Abell 1795 3C294 [700204] [800207] Abell 1835 Abell 2199 [800005] [800006] Abell 2204 MS2137-2353 Abell 2390 [800008] [800009]
Exposure (ks) 5.0 9.4 9.8 9.1 36.3 19.4 19.5 70.0 19.6 17.7 15.1 10.0 34.7 9.8 9.1
Detections 18 21 17 17 61 24 31 48 27 33 23 32 35 27 23
A C E chips analysed 023 2367 67 2367 23567 235678 2367 67 23678 23567 2367 235678 67 23567 23678
Hard (%) 9 (50) 10 [48j 6 (35) 5 (29) 28 (46) 5 (21) 12 (39) 24 (50) 11 (41) 12 (36) 7 (30) 13 (41) 9 (26) 8 (30) 4 (17)
Photometric redshifts of 51 AGN counterparts followed up with optical/near-infrared photometry peak a t z = 1.2 and extend t o z 4,with harder sources preferentially lying a t z < 1. The optical/near-IR Sleds of the hardest sources are dominated by host galaxy light, and are consistent with those of early-type hosts. Spectroscopic redshift confirmations of a sub-sample showed that the Zphot estimates were very good for the hard sources, and less reliable for the soft (AGN-dominated) X-ray sources. We identified 12 hard AGN as type 2 X-ray QSOs with intrinsic lumiN
233 p?
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Channel Energy (keV) Figure 1. X-ray spectrum of a Compton-thick QSO at z = 0.56 in the field of the cluster Abell 963. The dark circles show the spectrum extracted from Chandra ACIS (34 ks), while the filled, grey squares with error bars show the XMM-Newton MOSl data (25 ks). ~ and a redshifted Fe Ka: The solid line is a power-law fit with r = 2, N ~ = l o ’cm-’ erg s-l. line, detected in both instruments. The absorbed X-ray luminosity-
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nosity erg s-’. The sources have a median redshift z 2.1. Two are strongly lensed by factors of 2 and 8. X-ray spectral fitting/estimation reveals N H > cm-2 (= extinction A” > 60 assuming a Galactic dust:gas ratio) in several sources, and one Compton-thick QSO with NH = cm-2 (Fig. 1). The power inferred to be re-processed to the far-IR is 10l1 - 1013L0. This first, wide-area study of distant, X-ray selected QS02s enabled us to place a lower areal density limit of 12 sources deg-2.
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3. Completely obscured AGN The absence of strong emission lines in near-IR VLT and UKIRT spectra of several sources studied suggested the presence of high covering factors of dust extinction3. In fact, many of the newly-discovered XRB sources possess weak optical signs of activity suggesting that the obscuring material prevents radiation from escaping in any direction (‘elusive AGN’4). One such source is shown in Fig. 2, whose hard X-ray emission is that erg s-l at z = 0.38. The only emisof a Sy 2 with Lx 5x sion lines seen - [OIII]AX 4959, 5007 - are, however, unresolved, implying FWHM cm-2 (Fig. 3). This suggests that their elusive nature is associated with heavy obscuration.
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Figure 2. Fraction of elusive AGN, along with classical Seyfert nuclei, in different IR luminosity ranges
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Figure 3. Distribution of absorbing column densities for elusive AGN and classical Seyfert 2 nuclei. Note that elusive AGN tend to be much more absorbed than classical SY2
One possibility is that the Narrow Line Region is also obscured t o our line of sight4, so that we cannot detect the emission lines which allow to identify obscured AGN as in classical type 2 Seyferts. In this case one would expect to detect the high excitation narrow lines in the infrared, where dust extinction is much reduced. However, most elusive AGN spectroscopically observed so far in the IR do not show such lines. Fig. 4 shows the near-IR
238 spectrum of the elusive AGN UGC5101, which is characterized by the very red continuum and diluted stellar features (CO) typically observed in AGN and due t o hot dust emission; however there is no hint of the high excitation emission lines which are typically observed in this band in AGN. The more likely explanation is that in elusive AGN the nuclear radiation source is obscured in all directions, thus preventing UV photons t o escape and t o produce a Narrow Line Region. Another possibility is that dilution from the host galaxy in the optical spectra prevents us to identify the AGN emission lines. This may apply to distant systems, but certainly not to many of the very nearby elusive AGN investigated by us (e.g. NGC4945, NGC3690). L
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Figure 4. Near-IR spectrum of the elusive AGN UGC5101, showing the very red continuum and diluted CO stellar feature due to hot dust emission typical of AGN, but no coronal lines are observed.
These results were obtained within the context of a wider collaboration which includes scientists listed on the front page. We acknowledge partial support by the Italian Institute for Astronomy (INAF) and by the Italian Ministry for Research (MIUR).
References 1. 2. 3. 4. 5.
R. Della Ceca et al., A p J 581,L9 (2002). M. Guainazzi e t al., A&A 356,463 (2000). R. Maiolino et al., MNRAS 344,L59 (2003). R. Maiolino & G. H. Rieke, ApJ454, 95 (1995). A. Marconi et al., A&A 357, 24 (2000).
TRANSMISSION- TO REFLECTION-DOMINATED TRANSITION IN SEYFERT 2 GALAXIES: THE XMM-NEWTON VIEW*
M. GUAINAZZI AND P. RODRIGUEZ-PASCUAL XMM-Newton Science Operations Center, RSSD of E S A , VILSPA, Apartado 50727, E-28080 Madrid, Spain, E-mail: m g u a i n a z @ x m .vi l s p a . e s a . e s A.C. FABIAN AND K. IWASAWA Institute of Astronomy, Madingley Road, Cambridge, CB3 OHA G. MATT Dipartimento di Fisica ‘%.Amaldi”, Uniuersitd “Roma f i e ” , Via della Vasca Nauale, 1-00184 Roma, Italy F. FIORE INAF-Osservatorio Astronomic0 d i Roma, via Rascati 33, Monteporzio-Catone (RM), 00040, Italy
In this paper we present the current status of a XMM-Newton program t o observe an optically-defined, complete and unbiased sample of Compton-thick Seyfert 2 galaxies. The main goal of this project is the measurement of the occurrence rate of transition between transmission- (2. e. Compton-thin), and reflection-dominated spectral states. These transitions potentially provide information on the distribution of the obscuring matter surrounding the nucleus, and on the duty-cycle of the AGN activity. With about 2/3 of the whole sample being observed, we detected 1 further transition out of 8 observed objects, confirming previous suggestions that these transitions occur on time-scales -5Q-100 years.
*This work is based on observations obtained with XMM-newton, and ESA science mission with instruments and contributions directly funded by ESA member states and the USA (NASA).
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1. The unstable temper of Compton-thick Seyfert 2s
Our group is pursuing a XMM-Newton survey of an optically defined, complete sample of X-ray obscured nearby Seyfert galaxies, classified as Compton-thick according to observations prior t o the launch of Chandru and XMM-Newton. The main goal of this project is t o measure the occurrence rate of transitions between “transmission-” and “reflectiondominated” spectral states (Matt et al. 2003, and references therein). Traditional wisdom associates “reflection-dominated” states to AGN covered by a Compton-thick ( i e . N H 2 at1 N 1.5 x cm-2) absorber, which totally suppresses the AGN emission below 10 keV. The discovery of “transmission-” t o “reflection-dominated” state transitions (simply transitions hereafter: Guainazzi et al. 2002; Guainazzi 2002) fundamentally challenges this traditional wisdom, as well as - in a broader astrophysical context - a “static interpretation” of the Seyfert Unification Models. In at least two out of the five known cases (Guainazzi 2002; Gilli et al. ZOOO), these transitions are best explained with variations of the AGN intrinsic power by a t least one order of magnitude on timescales -years, as in the Narrow Line Seyfert 1 Galaxy NGC 4051 (Uttley et al. 1999). Matt (2000) proposed an extension of the standard Unification Models, whereby the nuclear, pc-scale torus is responsible for the Compton-thick absorption only, whereas the Compton-thin matter is located at much larger distances, possibly associated to the host galaxy rather than to the nuclear environment. In this paper we present preliminary results of this study, with 8 out of the foreseen 12 targets being already observed. 2. The XMM-Newton results
These transitions are not ubiquitous on the timescale roughly defined by the average interval between the ASCA/BeppoSAX, and the XMMNewton/ Chundra observations (a few years). The Circinus Galaxy and NGC 1068, the closest and best studied Compton-thick AGN known, exhibit a consistently reflection-dominated spectrum across their whole recorded X-ray history (Fig.l), with very little spectral changes. In Fig.2 we show a comparison between the ASCA/BeppoSAX and the XMM-Newton/ Chandra measurements of two of the observables, which identify a transition: a) a dramatic change in the Equivalent Width (EW) of the K, fluorescent iron line, from (less than) -100 to several hundreds/thousand eV; b) hard (e.g. 2-10 keV) X-ray flux changes by a factor
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Figure 1. X-ray Spectral Energy Distribution of the Circinus Galaxy (left) and NGC 1068 (right) as derived from their ASCA, BeppoSAX and XMM-Newton observations
23-5; The same observables are shown for UGC 4203 as well, the prototyp-
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Figure 2. Comparison between measurements of the K, fluorescent iron line EW (left) and the hard X-ray flux (right) between measurements done by ASCA/BeppoSAX (yaxis) and XMM-Newton/Chandra (x-axis). Objects from the XMM-Newton Comptonthick sample are indicated by filled dots, UGC 4203 (the prototypical "Phoenix Galaxy" with an empty square. The dashed-dotted lines indicate a factor of f 3 variation from the equality (solid) line.
242 ical “Phoenix Galaxy” (Guainazzi et al. 2002). Out of 8 objects observed by XMM-Newton so far, one (NGC 4939) exhibits a 2 factor of 10 change in the K, iron line EW, together with a moderate variation of the hard X-ray flux. This confirms previous results, suggesting that these transitions are detected in ~ 1 0 of % nearby Seyfert 2 galaxies, when ASCA/BeppoSAX and XMM-Newton/ Chundru observations are compared. Monte-Carlo simulations of Compton spectra produced by slabs with different column densities indicate that in NGC 4939 the absorber in the transmission-dominated and the reflector in the reflection-dominated state may have the same column density (Matt et al. 2003; cf. Fig. 3).
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Figure 3. Comparison between the absorber column density measured during transmission-dominated states and the hard X-ray hardness ratio measured during reflection-dominated states for all the objects showing a transition. The solid line indicates the expected relation according to Matt et al. (2003). Objects above the line have never been reflection-dominated, despite their formal classification. For objects below the line the absorber and the reflector cannot have the same column density, by contrast with a scenario whereby a compact and homogeneous torus covers the nucleus. To the latter group belongs NGC 6300 as well (Guainazzi 2002), on the basis of its E 2 10 keV RXTE spectrum.
References 1. R. Gilli et al., A&A 355, 485 (2000). 2. M. Guainazzi, MNRAS 329, L13 (2002). 3. M. Guainazzi, G. Matt, F. Fiore & G.C. Perola, A&A 388, 687 (2002). 4. G. Matt, A&A 355, L31 (2000). 5. G. Matt, M. Guainazzi & R. Maiolino, MNRAS 342, 422 (2003). 6. P. Uttley, I. McHardy, I.E. Papadakis, M. Guainazzi & A. Fruscione, MNRAS 307, L6 (1999).
PHYSICAL PROCESSES BEHIND THE ALIGNMENT EFFECT
S. MENDOZA AND J. C. HIDALGO* Instituto de Astronomia, Universidad Nacional Autdnoma d e Mdxico, A.P. 70-264, Ciudad Universitaria, Distrito Federal CP 04510, Mdxico E-mail:
[email protected], jch54 @cam.ac.uk
The radio/optical alignment effect for small powerful radio galaxies has been shown to be produced by shock waves formed by the interaction of the head of the jet and/or cocoon with clouds embedded in the interstellar/intergalactic medium. We present here preliminary results of analytical and numerical solutions that have been made to account for the production of implosive shock waves induced by embedding cold clouds in the radio lobe of expanding powerful radio sources.
1. Introduction The radio/optical alignment effect in powerful radio galaxies was first observed by Chambers and collaborators1i2 and has been extensively investigated by Best and collaborator^^^^^^^^. All these observations show powerful radio galaxies that display enhanced optical/UV continuum emission and extended emission line regions, elongated and aligned with the radio jet axis. The expansion of the radio source strongly affects the gas clouds in the surrounding intergalactic/interstellar medium. Best and his collaborators7 showed that the emission from small radio sources (5 150pc) were dominated by shocks most probably generated by the interaction between the bow shock of the jet and the surrounding medium. For large radio sources the emission appears to be the AGN itself. From the various theoretical models that have been proposed to account for the emission observed, one of the most exotic ones was the idea that the interaction of the jet with clouds embedded in the interstellar medium induced the formation of stars. Based on the original idea of Begelman' we have constructed a model in which implosive shock waves were driven *Current address: Churchill College, Cambridge CB3 ODs, United Kingdom.
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in the clouds after finding themselves immersed on very high pressure environments due to the passage of the jet.
2. Implosive shock-waves
When the head of an expanding extragalactic jet encounters clouds with much smaller radii than the radius of the jet, then one can think that the interaction hardly modifies the structure of the jet. The collision between the bow shock wave and/or the hot spot shock of the jet with clouds embedded in the interstellar and intergalactic medium is quite complicated. A very general 2D description of the collision between a plane parallel shock and a cloud was described in detailg. These calculations showed that after the passage of the shock wave, shocks and rarefaction waves are formed" which lead to the destruction of the cloud. At first approximation one can model the interaction of a shock wave with a cloud as follows. The clouds are originally in pressure equilibrium with their surrounding interstellar or intergalactic medium. After being swallowed by the expanding jet, the clouds find themselves on an overpressured medium'. If the post-shock pressure is sufficiently large as compared to the pre-shocked pressure one can guarantee the formation of an initial discontinuity that produces an implosive shock wave and an expanding rarefaction wave, leaving a tangential discontinuity which can now be identified as the border of the cloud. Well known similarity solutions for the problem of a non-relativistic explosive spherical shock waves have been found in the past12. A similarity solution for the problem of a relativistic shock wave was found by14. Both approaches, relativistic and non-relativistic are based on the idea that the energy content inside the shock wave is constant. Guderley" , Landau and S t a n y ~ k o v i c h ' ~found ~ ' ~ self-similar solutions for the case of a spherical shock wave converging to a centre, the so called implosive shock wave. For the case of a relativistic implosive shock wave we have found a similarity solution that generalises Landau & Staniukovich's model and takes into account some of the relativistic ingredients introduced by Blandford and McKee14 for the relativistic explosive shock wave. The complete mathematical description of this model will be described elsewhere. Here, we briefly mention the most important results. For this particular case, the Lorentz factor I' of the implosive shock wave is such that r2= A(-t)-", where the constant m represents the similarity index. Exactly as it happens for the non-relativistic implosive shock wave, due to
245 the fact that the energy is not conserved, one has to find the similarity index by demanding non-singularities on the equations of motion. By doing that and assuming a polytropic index K = 413 we found that m = 0.78460969. With this similarity index it was then possible to find numerical solutions for the density, pressure and velocity profiles of the post-shocked material.
3. Astrophysical consequences
With the model presented in Section 2 it is now possible to apply the results to typical clouds in the interstellar medium. Inside the jet of a typical FR-I1 radio galaxy, the velocity of the plasma is close to the velocity of light, and the equation of state of the plasma is p = e / 3 , where e is the proper energy density. The pressure inside the jet has a typical value of lOP5Pa. When this gas is shocked, the pressure grows to a very high value of 10-2Pa. Under these circumstances, when a cold ( w lOK) dense ( w 102cm-3) typical interstellar cloud with characteristic radius of 1 pc, finds itself inside the radio lobe of a radio galaxy, then an ultrarelativistic implosive shock wave is developed inside its structure. The post-shock temperature, immediately after the shock reaches values of 1013K. The particle number density at this point is 104cm-3. The cooling time ~~~~l of the post-shocked gas was calculated15 and its given by ~~~~l = 3.72 x 1014s. In comparison, the collapse time of the implosive the shock is able shock wave is ~ ~ =~ 1.13 1 x1 10%. Since ~~~~1 >> to collapse completely and even reach a situation of bouncing back as a kind of explosive shock wave. At the time of collapse the radius of the cloud diminishes to a value of 37600AU. When this stage is reached, the post-shock values for the pressure, density and temperature are found to be 0.01 Pa, 1500 cm-3 and 1.81x 1012Krespectively. Under this circumstances, the squared ratio of the post-shocked Jeans mass hfJ2 to the pre-shocked Jeans mass M J ~ of the cloud reaches a value of 6.6 x This means that the Jeans mass of the cloud grows on a very great proportion and so, a gravitational collapse can not occur at least for the adiabatic solution presented here. In summary, we have prooved that a gravitational collapse is not possible under the model presented here. So, under these circumstances no star formation is induced by the passage of the radio jet through clouds embedded in the interstellar medium of the host galaxy. However, this model suggests another form of shock radiation that might be presented when clouds get embedded in the radio lobes of powerful1 radio galaxies.
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It is important to note that radiation and self-gravity of the cloud was not included on our calculations. We intend to do a full 3D simulation including these physical ingredients in the future. Acknowledgements
S. Mendoza thanks support granted by CONACyT (41443). J.C. Hidalgo acknowledges the support granted by Fundaci6n UNAM. References K.C. Chambers, G.K. Miley & W. van Breugel, Nature 329, 15 (1987). P.J. McCarthy, W. van Breugel & H. Spinrad, ApJ 321, L33 (1987). P.N. Best, M.S. Longair & H.J.A. Rottgering, MNRAS 286 785 (1997). P.N. Best, C.L. Carilli, S.T. Garrington, M.S. Longair & H.J.A. Rottgering, MNRAS 299, 357 (1998). 5. K.J. Inskip, astro-ph/0306108, (2003). 6. K.J. Inskip, P.N. Best & M.S. Longair, New Astronomy Review 47, 255, (2003). 7. P.N. Best, H.J.A. Rottgering & M.S. Longair, MNRAS 311, 23 (2000). 8. M.C. Begelman & D.F. Cioffi, ApJ 345 L21, (1989). 9. R.I. Klein, C.F. McKee & P. Colella, ApJ420, 213 (1994). 10. S. Mendoza, Rev. Mez. Fis. 46, 391 (2000). 11. G. Guderley, Luftfahrtforschung 19 302 (1942). 12. K.P. Stanyukovich, Oxford University Press, Oxford, U.K., (1960). 13. L.D. Landau & E.M. Lifshitz, Fluid Mechanics, Course on theoretical Physics V.6, Pergamon Press, London, 2nd edition, (1987). 14. R.D. Blandford & C.F. McKee, Physics of Fluids 19, 1130 (1976). 15. J. Silk & R.F.G. Wyse, Physics Reports 231, 295, (1993).
1. 2. 3. 4.
UNCONVENTIONAL AGN FROM THE SDSS
P. B. HALL, G. R. KNAPP, G. T. RICHARDS AND M. A. STRAUSS Princeton University Observatory, Princeton, NJ 08544 S. F. ANDERSON Astronomy Department, University of Washington, Seattle, W A 98195
D. P. SCHNEIDER AND D. A. VANDEN BERK Dept. Astronomy & Astrophysics, Penn State Univ., University Park, PA 16802 D. G. YORK Astronomy Dept. & Enrico Fermi Institute, Univ. of Chicago, Chicago, IL 60637
K. S. J. ANDERSON, J. BRINKMANN AND S. A. SNEDDEN Apache Point Observatory, P.O. Box 59, Sunspot, NM 885'49
We discuss some of the most unusual active galactic nuclei (AGN) discovered t o date by the Sloan Digital Sky Survey (SDSS): the first broad absorption line quasar seen to exhibit He 11 absorption, several quasars with extremely strong, narrow UV Fe 11 emission, and an AGN with an unexplained and very strange continuum shape.
1. Introduction
The Sloan Digital Sky Survey (York et al. 2000; Fukugita et al. 1996; Gunn et al. 1998; Hogg et al. 2001; Stoughton et al. 2002; Smith et al. 2002; Pier of the et al. 2003) is obtaining optical spectra for -lo5 quasars over entire sky. Through careful target selection (Richards et al. 2002) and sheer size, the SDSS includes numerous AGN with unconventional properties. The high-quality, moderate-resolution SDSS spectra can be used to set the stage for the detailed multiwavelength studies often needed to understand interesting quasar subclasses. We illustrate this fact using several unusual AGN included in the SDSS Second Data Release (Abazajian et al. 2004).
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2. The first He11 A1640 broad absorption line quasar
Although broad absorption line (BAL) quasar outflows are known to include highly ionized gas (e.g., Telfer et al. 1998), He11 absorption had not been detected in them until this meeting (see Maiolino et al. 2004 for the second case). Figure 1 shows SDSS J162805.81+474415.6, a z=1.597 quasar with an outflow at v=8000 km s-l seen in C IV and He 11 X1640. He II A1640 is analogous to H I A6563 ( H a ) since it is the n=2-3 transition. The agreement between the velocity profiles of the C IV and the putative He 11 absorption is not exact, but is within the range of variation seen between troughs of different ions in BAL quasars (e.g., Arav et al. 2001). There is also a narrow system at z=1.4967 (v=11800 km ti-') seen in C IV, A1 11, Fe 11 and Mg 11 and an intervening, narrow Fe Ir+Mg 11 system at z = 0.9402. There are two other possible explanations for this trough. First, it could be due to A ~ I Iat I w=46000 km s-'; the lack of accompanying Mg11 absorption would not be unprecedented (Hall et al. 2002). Detection of C IV absorption at 3450A would confirm this hypothesis. Second, two SDSS quasars have Mg 11 absorption extending e l 5 0 0 km s-l redward of the systemic redshift (Hall et al. 2002); by analogy, this trough could be C I V redshifted by =7000 kms-' (without accompanying Mg11). That is an implausibly large velocity in terms of the redshifted absorption models discussed in Hall et al. (2002), but definitively ruling out this possibility
2000 3000 Rest Wavelength in Angstroms (log scale) Figure 1. The first He11 BAL quasar, SDSS 51628+4744. The ordinate in this and all ergs cm-' s-l k l . subsequent figures is flux density FA in units of
249 requires spectroscopy at 68As the median shows, the energy output of both radio-loud (RLQs) and radio-quiet (RQQs) AGN peaks in both infra-red (IR bump) and optical (“Big Blue Bump”) wavebands. The IR bump is attributed to thermal dust emission, and the Big Blue Bump to thermal emission from gas in an accretion disk (AD). The inflection between the two bumps, at N 1 . 5 m, ~ is likely due to dust sublimation N 2000K.56In the X-ray region, 50% of both RLQs and RQQs have a soft X-ray excess component attributed to the high energy tail of the Big Blue Bump. At harder X-ray energies, power law emission from RQQs typically has a slope, c t 1 . ~0 f 0 .~5 (F, c( the error indicates the observed range), while in RLQs the slope is flatter (- 0.51t0.5) and the relative normalisation about x 3 higher.70>52 The emission mechanisms are interpreted differently: comptonisation of EUV photons in the Big Blue Bump for RQQsl’ and Compton scattering of the radio photons in RLQs.~’ In low luminosity AGN (LLAGN) reflected and/or scattered emission from cold/hot material surrounding the X-ray source, such as an AD corona or the inner edge
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266 of a dusty t o r ~ s / d i s k often , ~ ~dominate ~ ~ ~ ~the ~ ~underlying ~ ~ ~ power law. Strong Fe K a emission, originating in cold and/or hot material, is present in many LLAGN but weaker/absent at higher l u m i n ~ s i t i e s .The ~ ~ X-ray emission peaks N 40 - 400, keV38, a third bump in the SED (Figure 2). The most notable difference between RLQs and RQQs is in the radio waveband. In RQQs the SED turns over sharply in the far-IR/mm and radio emission is N 100- 1000x weaker than in RLQs. The far-IR cut-off in RQQs is well-determined in a small number of far-IR-bright nearby sources. Constraints on its slope are frequently steeper than the Y ~characteristic . ~ of homogeneous synchrotron self-absorption and are interpreted as grey-body emission from cool d ~ s t . ~ ? ~ ~ Photon energy
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Frequency [ Hz ] Figure 2. The radio-y-ray SED of 3C273 on (a) F, and (b) vF, scale61 showing the smooth, radio-IR continuum emission typical of core-dominated RLQs.
By contrast, the far-IR emission from core-dominated RLQs smoothly extends into the radio, implying a significant/dominant non-thermal component in both wavebands (Figure 2). 3C273 exhibits the correlated variability characteristic of blazars (core-dominated RLQs viewed pole-on), but even here the lack of variability in the hottest part of the IR continuum indicates the presence of hot duskG1Comparison of the IR continua of RLQs and RQQs by ESA’s Infrared Space Observatory (ISO) suggests that nonthermal IR emission dominates pole-on RLQs but decreases in strength as the viewing angle increases so that thermal emission also contributes in
267 lobe-dominated R L Q S ~ ~ > ~ ’ . 1-
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Figure 3. mm-optical SED of PG1351+640 showing the wide range of temperature required to explain the full IR continuum as thermal emission from dust. The curves show grey body curves at the marked temperatures normalised to the data.
A few core-dominated, RLQs, (“blazars” such as 3C273, Figure 2) have and high energy Their SEDs have a fourth been detected in peak in the X-ray-y-ray regime which is comparable to or stronger than the Big Blue Bump so that y-rays potentially dominate AGN energy output. The radio, X-ray and y-ray radiation (at least) from these AGN is beamed along our line of sight and Doppler boosted due to high speeds in the jets. y-ray emission has been detected from only a small number of unbeamed AGN5, though ESA’s Integral mission may change this. 2.2. Origin of the various components
The physical picture for the origin of these components is based on Unification of the AGN c l a s ~ e sAn . ~ AGN’s ~ ~ ~ central, super-massive ( lo7-’ M g ) black hole is surrounded by hot accreting gas, primarily confined to an AD which emits optical and UV radiation t o provide the Big Blue Bump. The IR bump originates in dust with a wide range of temperatures (Figure 3), the hottest being directly associated with the AGN, again with a disk-like/torus geometry, while the cooler dust originates in the host galaxy. X-ray and core radio emission vary on short timescales ( w 1- 100 It. days) and so originate close to the central black hole, interior to the AD. Some AGN ( w 10%) have extended radio structure from jets and lobes on much larger scales which will not be discussed here. In a simple unification scenario broad-lined (Type 1) AGN are viewed face-on while narrow-lined (Type 2) AGN are viewed edge-on such that
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the broad emission lines, soft X-rays and much of the optical/UV emission from the AD are hidden by the dust (as for IR-selected AGN, Figure 1). Comparisons between the SEDs of Seyfert (Sy) 1 and 2 at low redshift show that Sy2s have less prominent Big Blue Bumps and stronger soft X-ray absorption than Syls, consistent with this scenario. To explain the broad IR continuum (Figure 3) using pure thermal emission, the dust must have a wide range of temperatures (- 50 - 1000K). Based upon the presence of extended dust emission in nearby AGN (e.g. Cen A15), strong correlations between hot mid-IR emission and the presence of an AGNZ4 and weaker correlations between far-IR emission and other AGN indicators,' the IR continuum has been modeled using 2/3 components. A hot, obscuring dusty disk/torus in an AGN4si19 produces a narrow continuum feature which is combined with a cooler, starburst c o m p ~ n e n t . ' ~Cool ? ~ ~dust in the host galaxy may also contribute.
Figure 4. AD models fitted to the SED of REJ1034+396 demonstrating that it is likely viewed edge-on (60-75deg), accreting at nearly Eddington rates (0.3-0.7L~dd)onto a low-mass black hole (MBH N 2 - 106Mo)51
3. How well does the picture fit? 3.1. The Optical/UV Big Blue Bump
The Big Blue Bump can be explained as thermal emission from gas in an AD with a wide range of temperatures, their large number of parameters can produce the variety of observed SED shapes.(Figure 451958)Individual fits which include the soft X-ray excess require scattering of the AD pho~ ~further ' ~ ~ constrain AD models, an tons in a lower density, hot c ~ r o n a .To
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observational relation between optical/UV colors and black hole mass is required. Mass measurements are available for a small number of low-redshift sources, although new methods for higher redshift AGN are now a ~ a i l a b l e . ~ ~ New models invoking mildly optically thick cloud distributi~nsll>~ provide an alternative explanation for the optical-soft X-ray continuum of AGN. 3.2. IR continuum
Spectroscopic observations from IS0 show a stronger near-mid IR continuum in Syl than in Sy2 galaxies causing a lower observed equivalent width 7.7 pm feature in S y h 8 Orientation dependent near-IR emission is also clear from comparison of Sy2s with and without hidden broad line regions25. Comparison with type 1 AGN (Figure 529), indicates obscur23, as opposed to 24 in earlier torus ing column densities, log NH models.48 Lower column density29 or models for the obscuring material can reproduce the full IR continua with orientation primarily responsible for the range in shapes. This removes the need for a starburstrelated component29 although a two-component model is required in some low-redshift AGN.15 Alternatively evolution, in which IR galaxies are young quasars/AGN where dust obscures the central engine,57may explain part/all the range in IR continuum shapes.22 As the AGN ages it’s SED changes from a young state where the far-IR continuum dominates, to an AGN state with a hotter IR continuum and Big Blue Bump, to a dead AGN with no Big Blue Bump. Although this model can explain the range of SEDs observed in the PG sample,22 there is no evidence connecting SED shape and redshift/age.
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3.3. Orientation, Obscuration, A G N Class and Luminosity
The unification scenario is supported statistically by the tendency for type 2 AGN to have absorbed X-ray spectra,62i2a redder optical continuum, and stronger galactic spectral features. But individual sources are less straightforward. Optical dust reddening is generally lower than the equivalent Xray gas a b s ~ r p t i o nSources . ~ ~ ~ ~have ~ been seen to change type, with broad emission lines appearing/disappearing and/or X-ray absorption varying.37 Some type 1 or intermediate sources have strong X-ray absorption47 and there is little relation between X-ray hardness ratio and AGN c l a d 7 (Figure 6). These results imply a more complex obscuring medium such as a high velocity, accelerating wind originating in a disk.28>42i13 These models can also explain the high excitation, broad-absorption lines visible in 10% N
270 , mwcI
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Figure 5. Left: Mid-1R colors for type 1 AGN and Sy2 galaxies25 showing that re23 can explain the progression2'. Right: Optical colors for denning of up to log NH LLAGN, dashed line shows changing color with increasing galaxy c ~ n t r i b u t i o n . ~ ~
of type 1 AGN. Clumpiness and variation in the wind, combined with differing lines-of-sight to continuum and line regions, can explain most properties of individual sources, although explanations for the combination of broad lines and X-ray absorption seem contrived. To provide real constraints on the structure and geometry of the absorbing material, a systematic, multiwavelength study of intermediate sources is required.
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Figure 6. Chandra X-ray hardness ratios vs. optical class for 2MASS Sy2s, which have lower luminosity and higher obscuration than Syls, often show optical/UV host galaxy spectral features. Galaxy light peaks
271
in the wavelength region between the IR and OUV bumps in AGN so the
strength of the inflection depends on the relative luminosity of the AGN and its host. Thus the near-IR is the best region in which to study the host galaxy.3gHost galaxy emission may also contribute to the near- and mid-IR and optical continua(Figure 533), hiding AGN features in these regions. 3.4. Ingredients which determine the Shape of the SED Many parameters are important in determining the observed shape of an AGN SED. The relative luminosities of the AGN itself, related to the black hole mass, and of its host galaxy determine the visibility of host galaxy emission. The accretion rate and physical properties of the AD combine with its inclination to our line-of-sight to determine the shape and strength6g of the Big Blue B ~ m p . ~The ~ >amount, ~ ~ 2geometry, ~ ~ ionisation, optical depth and inclination of absorbing dust and gas determine the IR continuum and the absorption of the optical, near-IR and soft X-ray continua. The amount and location of scattering material and the strength of the scattered light is also important in edge-on (type 2) AGN where the primary AGN continuum is partially/fully obscured." The presence and strength of a radio source in the AGN core affects the radio, far-IR and hard X-ray continua. One property which, perhaps surpisingly, shows no relation to the SED is redshift. The central black hole, the primary energy source, is expected to grow as material accretes causing the observable properties of the AGN to evolve. While the OUV and IR SEDs are diverse, there is currently no evidence for a redshift Samples are limited and the new, greater accessibility of high redshift AGN in many wavebands will provide significant new data on their evolution. 4. Our Expanding View of AGN
With so many variables, the similarity of AGN SEDs is perhaps more surprising than their diversity. But are they mostly similar because we select them to be? Would we recognise an AGN that was, for example, so heavily absorbed that few if any AGN characteristics are visible? Host galaxy light may dominate optical AGN signatures in Sy2s and hide a significant fraction of the p ~ p u l a t i o n as , ~demonstrated ~ by the presence of X-ray luminous galaxies in Chandru survey^.^^^^ Perhaps the most critical question is L L Hdo ~we~ know we have an AGN?" New AGN are being found in radio,65 IR" and deeper optical surveys, 2DF and SDSS.53Models for the Cosmic X-ray Background (CXRB)
272 require a new population of X-ray absorbed AGN.17 Chandra and XMMNewton find X-ray sources sufficiently luminous t o be AGN but with no optical AGN characteristics. Bright radio galaxies with strong, unresolved cores show no optical AGN signature^.^^ Are these all AGN? If so how do they relate t o more standard AGN? What set of properties define an AGN? How can we observe the parent population? The next generation of multi-wavelength surveys will answer many of these questions, providing both deep, small areas (GOODS?) and shallower, wider areas (SWIRE;31 ChaMP27)t o sample overlapping subsets of the AGN population. The combination of sensitive IR and X-ray, provided by Chandra, XMM-Newton and Spitzer, is particularly powerful. Spitzer sees all luminous IR sources while the X-rays select the AGN from amongst the dominant IR galaxy population. These are exciting times!
References 1. Andreani, P. et al., 2003, A J , 125, 444 2. Awaki, H. et al., 1997, AdSpR, 19, 95 3. Barthel, P.D., 1989, ApJ, 336, 606 4. Brandt, W.N., et al., 2002, ApJ, 569, 5 5. Beilicke, M., Goetting, N. & Tluczykont, M., NewAR 48, 407 6. Brandt, W. N., et al., 2001, AJ, 122, 2810 7. Chini, R., Kreysa, E. & Biermann, P.L., 1989, AA, 219, 87 8. Clavel, J. et al., 2000, AA, 357, 839 9. Collin-Souffrin, S. et al., 1996, AA, 314, 393 10. Cutri, R.M. et al., 2002, ASP Conf. Ser. 284, 127 11. Czerny, B. & Dumont, A-M., 1998, AA, 338, 386 12. Efstathiou, A. & Rowan-Robinson, M., 1995, MNRAS, 273, 649 13. Elvis, M.S., 2000, ApJ, 545, 63 14. Elvis, M., Wilkes, B.J., et al. ApJ, 95, 1 (1994) 15. Genzel, R. & Cesarsky, C.J., 2000, ARAA, 38, 761 16. Giavalisco, M. et al., 2004, ApJL, 600, L93 17. Gilli, R., Salvati, M. & Hasinger, G., 2001, AA, 366, 407 18. Gondek, D. et al., 1996, MNRAS, 282, 646 19. Granato, G.L. & Danese, D.L., 1994, 268, 23 20. Green, P.J., et al., 2004, ApJS, 150, 43 21. Ham, M. et al., 1998, ApJ, 503, L109 22. Haas, M. et al., 2003, AA, 402, 87 23. Hartman, R.C., et al., ApJS, 123, 79 24. Heisler, C.A. & de Robertis, M.M., 1999, AJ, 118, 2038 25. Heisler, C.A., Lumsden, S.L. & Bailey, J.A., 1997, Nat., 385, 700 26. Hughes, D.H. et al., 1993, MNRAS, 263, 607 27. Kim, D-W., 2004a, ApJ, 600, 59 28. Konigl, A. & Kartje, J.F., 1994, ApJ, 434, 446
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274
Jennifer Scott, Gordon Richards and Sarah Gallagher
The UNAM table
X-RAY WEAK QUASARS: ABSORPTION OR AN INTRINSICALLY DIFFERENT SED? *
G. R I S A L I T I ~ M. ~ ~ ,ELVIS~AND E.
MEMO LA^
Harvard-Smithsonian Center for Astrophysics
60 Garden Street, Cambridge, MA 02138, USA
INAF - Osservatorio Astrofisico di Arcetri L.go E. Fermi 5, 50125 Firenze, Italy
We present Chandra and XMM-Newton spectra, and optical and IR photometry of a sample of spectroscopically selected X-ray weak quasars. We discuss intrinsically different SEDs and obscuration as the two possible explanations for the low observed X-ray to optical ratio. We show that there is no obvious way to reproduce the observational data assuming an intrinsically standard emission and some kind of obscuration, even allowing for a dust-to-gas ratio different from Galactic. We conclude that our objects are likely to represent a class of intrinsically peculiar quasars, with a low X-ray emission and relatively red optical colors.
1. Introduction Optically selected quasars show a remarkable homogeneity in their X-ray properties. The 1-10 keV continuum of broad line quasars is well reproduced by a power law with I? ~ 1 . 9 - (George 2 et al. 2000, Mineo et al. 2000)”. The X-ray to optical ratio is usually measured with sox, defined as the slope of a power law connecting the monochromatic luminosity a t 2500 lo, and the one a t 2 keV, I x . For local P G quasars QOX -1.55 f 0.2 (Laor et al. 1997). There is now convincing evidence that more luminous quasars are fainter in the X-rays, with respect t o the optical (Zamorani et al. 1981, Avni & Tananbaum 1986, Wilkes et al. 1994, Yuan et al. 1998, Vignali et al. 2003). These results are all relative to color-selected objects. Blue optical/UV selection is quite efficient, but by no means complete. Many quasars could exist with optical colors similar to those of stars or galaxies.
A,
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‘This work is supported by NASA grant NAG5-12932 aBAL quasars, representing 10-20% of the quasar population, are an exception, with flat and weak X-ray emission.
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276 These objects would be missed by classical optical surveys, and even by recent multi-color surveys, like the 2dF (Croom et al. 2004). An example of how different selection criteria can unveil quasars with peculiar properties is the near-IR search for red quasars in the 2MASS Survey, based on the J-K color. Cutri et al. (2001) discovered a population of broad line, optically red quasars, as numerous as the local optically selected PG quasars. The X-ray emission of these objects was found to be extremely faint in Chandra observations (Wilkes et al. 2002). In order to search for quasars with different optical properties, we crosscorrelated a sample of spectroscopically selected quasars from the Hamburg Survey (HS, Hagen et al. 1995) with the ROSAT WGA Catalogue of pointed observations (White et al. 2000). Spectroscopic selection consist in choosing objects with broad emission lines in low resolution grism spectra, for slit spectroscopy follow-up. In this way, it is possible to discover quasars with intrinsically different optical SED (i.e. with a red continuum and broad emission lines) or with a standard SED plus moderate absorption (1-2 magnitudes absorption is enough to significantly redden the continuum, but broad emission lines can still be detectable). Our results (Risaliti et al. 2001) show that at least half of the so-selected quasars are soft X-ray weaker than “standard)) quasars by factors from 5 to 100. In order to better understand the nature of these sources, we obtained Chandra observations for 20 of them (preliminary results are presented in Risaliti et al. 2003) and, more recently, XMM-Newton follow-up observations for 8 of the Chandra targets. Moreover, we retrieved optical and near-IR colors from the POSS and 2MASS surveys, and we are starting an optical and near-IR spectroscopic follow-up of the most interesting objects. Here we discuss the preliminary results of this on-going project.
2. X-ray observations
The result of the cross-correlation of the HS quasars with the WGACAT is a sample of 80 objects with ROSAT pointed observations. About half of these sources were not detected by ROSAT, implying an X-ray weakness of a factor 5-100 with respect to standard quasars (Risaliti et al. 2001). We selected a subsample of 17 of these X-ray weak sources (plus 3 “control sources”) for Chandra follow-up. Out of these 17 sources, 3 turned out to be “normal” in terms of X-ray to optical ratio, implying high X-ray variability by factors of 10-50. We will not discuss these sources here. For 4 of the remaining 14 sources we also have XMM-Newton observations. N
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The main results of the spectral analysis are the following: 0 Out of 14 sources, 13 were detected by Chandra. Most of them are confirmed to be extremely faint in the X-rays. The X-ray to optical ratio is shown in Fig. l a , compared with that of optically selected quasars. 0 The Chandra X-ray spectrum is in all but one case well reproduced by a simple power law with no absorption. The photon index in on average slightly flatter that in optically selected quasars (FA" 1.5, t o be compared 2). However, the upper limits on the absorbing column density, with r N H , are rather high, due t o the low S/N. For this reason, we investigated the absorption scenario, fixing the photon index to the standard value, r = 2, and leaving N H free. We obtained N H best fit values in the range loz1 - 5 x 10" cm-2, and a significant correction in the estimate of the intrinsic OOX, as shown in Fig. l b . 0 The 4 XMM observations confirm the above results, adding more details. In all cases no significant variability has been detected. For one source, HS 0854+0915, which appears flat r 1 and extremely weak (sox = 2) when observed with Chandra, the higher S/N XMM-Newton spectrum shows a "normal" (I? 1.8) continuum, absorbed by a column density N H 6 x cm-' (Fig. 2). After correcting for this absorption, the intrinsic X-ray to optical ratio (sox = 1.67) is typical of standard blue quasars with the same optical luminosity (lo N 31). Briefly, the results of the Xray observations can be interpreted in two different ways: 1) unabsorbed,
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intrinsically faint power law continua, or 2) intrinsically normal spectra with absorption between 1021 and a few lo2’ cm-2. The first interpretation is directly suggested by the best fit models, which do not require absorption; the second one is worth mentioning because it would imply an intrinsically normal X-ray to optical ratio (Fig. lb). In order to further investigate these scenarios, we need either better quality X-ray spectra, or observations at other wavelengths. 3. Optical and infrared data The optical 0 and E magnitudes (similar to the standard B and R magnitudes) can be obtained from the digital Palomar All-Sky Survey. Infrared J, H and K magnitudes are available from the 2MASS Survey. In Fig. 3a and 3b we plot the 0 - E and J-K colors versus redshift, compared with the expected values for standard blue quasars (we used the SED of Elvis et al. 1994) with different values of extinction. The optical color of most objects is redder than in normal quasars, and corresponds to A v 1, if we assume a standard optical SED. On the other side, the infrared color is typical of standard, unobscured quasars. In order to obtain further information on the optical/near IR emission of our objects, optical spectroscopic observations are on-going at the HobbyEberly Telescope, and near-IR spectra are being obtained at the Italian 4meter TNG telescope. At present, only two near-IR spectra are available. In one of them the ratio of the redshifted broad Balmer lines suggests N
279
obscurationb, whereas the other one is a typical spectrum of unabsorbed quasars. 4. Discussion
Hard X-ray observations are in most cases well reproduced without any need of absorption in addition to Galactic, even if absorption cannot be ruled out, due to the poor S/N of most of our spectra. Moreover, assuming that a significant column density is present in most sources, and that the intrinsic emission is that of color-selected blue quasars, inconsistencies with observations at other wavelengths are found. In particular, one could assume that a low dust-to-gas ratio absorber is responsible for the observed X-ray weakness and the red optical color. This working hypothesis could explain the X-ray and optical continua, and the presence of broad emission lines in the optical, since an Av = 1 extinction still makes possible to detect strong emission lines. However, this is not in agreement with the infrared colors (we note that all our objects are bright quasars, therefore the contribution of the host galaxy to the observed colors should be negligible). Moreover, in the case of Av 1, the intrinsic flux in the B band (used to estimate the QOX index) would be 4 times higher than observed. This would imply an X-ray to optical ratio smaller by the same factor (corresponding to Aaox = 0.23). After this correction, the intrinsic QOX distribution would be again similar to that plotted in Fig. l a , i.e. the sources would still be X-ray weak. Summarizing, our data suggest that a significant fraction (at least 30%) of spectroscopically selected quasars have an intrinsically different spectral energy distribution with respect to optically selected blue quasars. We cannot rule out that absorption plays a role in at least part of our sample, however even in this case a standard intrinsic SED is unlikely. More data will be avalilable in the near future (optical and near-IR spectra, and hopefully deeper X-ray observations), which will help to solve the puzzle of a possible anomalous Spectral Energy Distribution. N
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Acknowledgements This work has been partially supported by NASA grant NAG5-12932. GR wishes to thank Raul Mujica and Roberto Maiolino for a really exciting bNote however that the ratio of broad Balmer lines could be not reliable, since the lines regions. ) are emitted in high-density (1O’O - 10” ~ m - ~
280
Figure 3. Optical and near-IR colors versus redshift, compared with the expectations for an intrinsically normal SED with different obscuration, as indicated in the labels.
meeting, both from a scientific and recreational point of view.
References 1. Y . Avni & H. Tananbaum, ApJ 3 0 5 , 83 (1986). 2. W. Cash, ApJ 2 2 8 , 939 (1979). 3. S.M. Croom et al., MNRAS in press (2004). (astro-ph/040340) 4. R. Cutri et al., in The New Era of Wide Field Astronomy, Eds. R. Clowes, A. Adamson, & G. Bromage ASP Conf. Ser. 2 3 2 , 78 (2001). 5. M. Elvis et al., A p J S 9 5 , 1 (1994). 6. I.M. George et al., ApJ 5 3 1 , 52 (2000). 7. H.-J. Hagen, D. Groote, D. Engels & D. Reimers, A B A S 111,195 (1995). 8. A. Laor et al., A p J 4 7 7 , 93 (1997). 9. T. Mineo et al., A&A 3 5 9 , 471 (2000). 10. G. Risaliti et al., A B A 3 7 1 , 37 (2001). 11. G. Risaliti et al., ApJ 5 9 5 , L17 (2003). 12. C. Vignali, W.N. Brandt & D.P. Schneider, AJ 1 2 5 , 433 (2003). 13. N.E. White, P. Giommi & L. Angelini, VzzieR Online Data Catalog (2000). 14. B.J. Wilkes et al., ApJS 9 2 , 53 (1994). 15. B.J. Wilkes et al., ApJ 5 6 4 , L65 (2002). 16. W. Yuan, J. Siebert & W. Brinkmann, A&A 3 3 4 , 498 (1998). 17. G. Zamorani et al., ApJ 2 4 5 , 357 (1981).
INFRARED SEDS OF QUASARS & RADIO GALAXIES: UNIFICATION AND DUST EVOLUTION SEEN BY ISO, SCUBA AND MAMBO
M. HAAS Astronomisches Institut der Ruhr- Universitat Bochum (AIR UB), Universitatsstr. 150, NA7, 0-44 780 Bochum, Germany E-mail:
[email protected] Sensitive Infrared SEDs drawn from the IS0 data archive and supplemented by SCUBA and MAMBO observations provide evidence for the geometric unification of powerful 3CR radio galaxies as ”edge-on” quasars. Fhrthermore, detailed SEDs of 64 Palornar-Green quasars show a diversity of shapes, consistent with the physical evolution of the dust distribution and the heating sources.
1. Powerful 3CR radio galaxies and quasars
1.1. Introduction and data The aim is to test the aspect-angle unification proposed by Barthel (1989): Powerful Fanaroff-Riley FR 2 radio galaxies are “edge-on” quasars viewed at high inclination, so that their nuclei are hidden behind a dust torus. If so, then this torus intercepts the optical-ultraviolet AGN radiation and reemits it in the infrared. Therefore a robust check of the unification is to look for the mid- and far-infrared reemission of the absorbed light from the AGN. A great advantage is that at wavelengths X>25 pm the IR emission is largely optically thin, hence isotropic and independent of the aspect angle. The 3CR catalogue of radio galaxies and quasars is selected at 178 MHz which measures the isotropic not-beamed emission of the radio lobes, hence the 3CR sources provide a well suited database to test the unification. While IRAS data of 3CR sources did not allow for drawing definite conclusions about the unification (Heckman et al. 1992; 1994; Hes, Barthel & Hoekstra 1995; Hoekstra, Barthel & Hes 1997), first results on small samples have been derived from I S 0 data (Haas et al. 1998; van Bemmel et al. 2000; Meisenheimer et al. 2001; Andreani et al. 2002). Here we consider the full ISOPHOT database of 75 sources in the I S 0 Data Archive, 281
282 supplemented by SCUBA archive data and new MAMBO observations. The results are presented in detail by Haas et al. (2004). They refer to 35 good detections, 16 radio galaxies and 19 quasars. We consider the following two basic source classes: i) the steep spectrum quasars and the BLRGs, henceforth for short denoted as quasars, and ii) the FR2 NLRGs, henceforth denoted as galaxies. The strategy to check the unification includes two steps: (1) to show that both the quasars and the galaxies exhibit a high mid- to far-IR luminosity ratio typical for AGNs, and (2) that the isotropic FIR-to-radio luminosity ratio is the same for quasars and galaxies at matched isotropic 178 MHz radio power. 1.2. Results Figure 1 shows SED examples for a quasar (3C 351), a galaxy (3C 234) and a starburst ULIRG (IRAS 17208-0014, from Klaas et al. 2001). With regard t o the FIR emission, the MIR emission of both the quasar and the galaxy is high, while that of the SB-ULIRG is low. Starbursts typically do not provide such a high LMIR/ LFIR ratio as powerful AGNs do.
Quasars
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Figure 1. SED examples.
Figure 2 shows the LMIR/LFIR ratio for the samples. This ratio is higher for the 3CR sample than for starburst-ULIRGs (from Klaas et al. 2001). This provides evidence for the presence of a powerful AGN in the galaxies as well. So far we have found evidence for a powerful AGN in both the quasars and the galaxies. In a strict sense, however, the concept of unification requires that for an object drawn from the parent population any isotropic emission remains the same while rotating the viewing angle to its axis. Thus, for an ideal sample of parent objects the emitted isotropic FIR dust
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power should be the same for objects of identical isotropic lobe power. Therefore we consider hr,the ratio of v F, at FIR wavelength 70 pm (= 4.3 THz) and v F, at radio frequency 178 MHz. Figure3 shows Rdr versus the 178 MHz radio lobe power. All along
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the range of the 178 MHz radio lobe power, the distribution of Rdr for the quasars is strikingly similar as that of the galaxies. This provides clear evidence in favour of geometric unification. Nevertheless, there is a considerable dispersion in the dust/lobe power ratio, which points toward the additional influence of the environment (e.g. for 3C 405) and evolution (e.g. for 3C321 and 3C459) of the sources. 2. Evolution of the dust emission of P G quasars
2.1. Introduction and data Extending Sander et al.'s idea (1988), that a quasar is preceded by a dusty ULIRG phase, the dust should not disappear at once and its relicts should trace evolutionary steps among the quasars. While former IR data did not allow the recognition of definite detailed signatures (due to limited sensitivity, wavelength coverage or sample size), here we show that such signatures can be identified for the first time in the sensitive I S 0 data of 64 PG quasars. The results are presented in detail by Haas et al. (2003). 2.2. Results
Actually the SEDs exhibit a diversity of shapes, as shown in Fig. 4. The observed SEDs reflect both the dust distribution around the heating sources and the nature of the heating sources as illustrated schematically, too. Firstly, we consider the physical processes acting on an initially irregular dust distribution. Dissipative cloud collisions and angular momentum constraints lead to the organisation of dust clouds into a torus/disk like configuration. With regard to the emission, the dust which is initially heated by starbursts will be powered more and more by the AGN, until the black hole (BH) begins to starve. Therefore it is natural to interpret the diversity of SEDs in terms of evolution. In Fig. 4 the SEDs a arranged along the expectations for such an evolutionary scheme (from top to bottom). During the evolution the corresponding SEDs show an initial FIR bump, then an increase in MIR emission and a steepening of the infrared slope, both of which finally also decrease. The AGN strength grows, then stays high and finally declines, as is marked by the size of the * and shows up in the SEDs by the optical slope. The PG quasars are practically not extinguished (A" < 0.3). Furthermore, the optical slope aoptis independent of IR properties like the nearto mid-IR slope ~ I (Fig. R 5). Therefore, with regard to the unified schemes we can assume a nearly face-on view onto the PG quasars.
285
Figure 4. Observed SEDs and scheme of dust distribution surrounding the AGN.
To conclude, the observed variety of SEDs can be associated with and sorted into physically meaningful classes, which reflect the amount and distribution of the reprocessing dust around the AGN. These classes can naturally be understood as a consequence of evolution of the quasars’ dust distribution and heating. Extending the known general evolutionary link between ULIRGs and quasars, the sensitive IS0 data allow for establishing the dust evolution even among the PG quasars.
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Acknowledgments
M. H. thanks for support from the Nordrhein-Westfalische Akademie der Wissenschaften, funded by t h e Federal S t a t e Nordrhein-Westfalen a n d t h e Federal Republic of Germany.
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(1994). 8. R. Hes, P.D. Barthel & H. Hoekstra, A&A 303, 8 (1995). 9. H. Hoekstra, P.D. Barthel & R. Hes, A&A 319, 757 (1997). 10. U. Klaas et al., A&A 379, 823 (2001). 11. K. Meisenheimer et al., A&A 372, 719 (2001). 12. D.B. Sanders et al., ApJ 325, 74 (1988) 13. I.M. van Bemmel, P. Barthel & Th. de Graauw, A&A 359, 523 (2000).
THE 2 > 4 QUASAR POPULATION OBSERVED BY CHANDRA AND XMM-NEWTON
c. VIGNALI* INAF-Osservatorio Astronomic0 di Bologna, Via Ranzani, 1 - I-401.27 Bologna, Italy E-mail: chrisQastro.psu. edu W.N. BRANDT AND D.P. SCHNEIDER Department of Astronomy & Astrophysics, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802, USA E-mail: niel,
[email protected]. edu
The current status of our Chundru and XMM-Newton project on high-redshift (2 2 4) quasars is briefly reviewed. We report the main results obtained in the last few years for the X-ray detected quasars, along with a few (M 10%) intriguing cases where no detection has been obtained with Chandra snapshot observations.
1. Introduction Quasars at z 2 4 provide direct information on the first massive structures to form in the Universe. The last few years have evidenced incredible progress in the study of the high-redshift Universe, largely thanks to ground-based optical surveys. In particular, the Sloan Digital Sky Survey (SDSSl) has discovered large numbers of high-redshift quasars, increasing the number of known quasars at z ;L 4 to > 500,2and many more are expected to be discovered before the survey ends (see [3] for the recent advances provided by the SDSS). Many of the high-redshift quasars discovered by recent optical surveys are suitable for follow-up X-ray investigations. Here we review X-ray studies of the highest redshift quasars, focusing on recent advances enabled largely by the imaging and spectroscopic capabilities of Chandra and X M M - N e w t o n . ‘Work partially supported by the Italian Space Agency under the contract AS1 I/R/057/02 (CV) and by the Chandra X-ray Center grant G02-3134X (WNB).
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Our knowledge of the X-ray properties of z 2 4 quasars has advanced rapidly over the last few years. Since the pioneering work based on the systematic analysis of archival ROSAT data4, where the number of X-ray detected quasars at z > 4 doubled, the progress made in this field has been substantial (see Fig. 1). At present, more than 90 quasars at z 2 4 have X-ray detections;" while in most cases Chandra snapshot (typically 4-6 ks) observations have allowed derivation of basic X-ray information (X-ray fluxes and luminosities),5~6~7~8~9~10~11~12i13 for a few X-ray luminous objects medium-quality X-ray spectra have also been obtainedl4tl5 thanks to the large collecting area of XMM-Newton. F'rom a general perspective, the most important results from X-ray analyses of high-redshift quasars are the following: o The X-ray properties of z 2 4 quasars are similar to those of local quasars. Joint X-ray spectral fitting of optically luminous quasars at z 2 4 selected from the Palomar Digital Sky Survey (DPOSSl') and the SDSS has shownl0?l1that quasar X-ray continuum shapes do not show evidence for aSee http://www.astro.psu.edu/users/niel/papers/highz-xray-detected.datfor a regularly updated listing of X-ray detections and sensitive upper limits at z 2 4.
289
significant spectral evolution over cosmic time. This has found further support recently via joint spectral fitting of a sample of 46 radio-quiet quasars (RQQs) with Chandra detections in the redshift range 4.0-6.3 ( x 750 source counts; r = 1.9 f O.l)l' and by direct X-ray spectral analyses of a few objects observed by XMM-Ne~ton.'~t'~ No evidence for widespread X-ray absorption has been found, although some quasars (see discussion below) are likely to be obscured. o The optical-to-X-ray properties of high-redshift quasars and those of local quasars have been found similar, once luminosity effects and selection biases are taken into account properly.18 Overall, the emerging picture is that the small-scale X-ray emission regions of quasars appear relatively insensitive to large-scale environmental differences at z x 6. o Moderately deep Chundra observations and the ultra-deep (2 Ms) survey in the Chandra Deep Field-North (CDF-N)" have allowed X-ray studies of moderate-luminosity AGN at z > 4; this population of AGN is more numerous and thus more representative than the rare, highly luminous quasars.20 o Similarly to the results obtained for the RQQs, neither the X-ray spectral slope (I' M 1.6 f 0.1) nor the jet emission of the radio-loud quasar population seems to evolve with cosmic time.21 No evidence for significant X-ray brightening ascribed to inverse Compton scattering of energetic electrons with Cosmic Microwave Background photons has been revealed by snapshot observations with Chandra.zl
3. X-ray non-detections: space oddities at high redshift?
At present, the fraction of X-ray upper limits among the sensitive Chandra and XMM-Newton observations of high-redshift quasars is low ( x 10%). About half of the X-ray undetected quasars are broad absorption-line quasars (BALQSOs), which are known to be absorbed in the X-ray band;z2 one quasar shows narrow absorption features from N V and Lya at approximately the source redshift.'l For most of these objects the lack of X-ray detections at the flux limits reached by Chandra with snapshot observations is likely due to absorption by column densities larger6I1' than x cm-' (assuming reasonable values for the optical-to-X-ray spectral energy distribution and X-ray photon index). It is possible that the remaining X-ray undetected high-redshift quasars are characterized by absorption features not recognized in low-resolution optical spectra. Recently, it has been shown that near-infrared spectroscopy can be highly effectivez3in de-
290 tecting absorption features in high-redshift objects previously classified as “normal” quasars. Clearly, minority AGN populations at z > 4 need to be investigated better in the X-ray regime. These include BALQSOs (whose number is still too limited t o derive statistically reliable average properties) and the population of quasars lacking emission line^.^^^^ Follow-up observations of quasars without optical emission lines with Chandra are on-going and the results will be presented in a forthcoming paper.25
References D.G. York et al., A J 120,1579 (2000). X. Fan, private communication (2004). K. Abazajian et al., AJ submitted, (2004). (astrc+ph/0403325) S. Kaspi, W.N. Brandt & D.P. Schneider, A J 119,2031 (2000; KBSOO). W.N. Brandt et al., AJ 121,591 (2001). C. Vignali, W.N. Brandt, X. Fan, J.E. Gunn, S. Kaspi, D.P. Schneider & M.A. Straws, A J 122,2143 (2001). 7. W.N. Brandt et al., A p J 569,L5 (2002). 8. J.D. Silverman et al., A p J 569,L1 (2002). 9. J. Bechtold et al., ApJ 588,119 (2003). 10. C. Vignali, W.N. Brandt, D.P. Schneider, G.P. Garmire & S. Kaspi, A J 125, 418 (2003). 11. C. Vignali et al., A J 125,2876 (2003). 12. F.J. Castander, E. Treister, T.J. Maccarone, P.S. Coppi, J. Maza, S.E. Zepf & R. Guzman, AJ 125,1689 (2003). 13. E. Treister, F.J. Castander, T.J. Maccarone, D. Herrera, E. Gawiser, J. Maza & P.S. Coppi, ApJ 603,36 (2004). 14. E. Ferrero & W. Brinkmann, A&A 402,465 (2003). 15. D. Grupe, S. Mathur, B.J. Wilkes & M. Elvis, A J 127,1 (2004). 16. S.G. Djorgovski et al., in Wide Field Surveys in Cosmology, 89 (1998). 17. C. Vignali, W.N. Brandt & D.P. Schneider, in AGN Physics with the Sloan Digital Sky Sumrey, in press, (2004). (astro-ph/0310659) 18. C. Vignali, W.N. Brandt & D.P. Schneider, AJ 125,433 (2003). 19. D.M. Alexander et al., A J 126,539 (2003). 20. C. Vignali, F.E. Bauer, D.M. Alexander, W.N. Brandt, A.E. Hornschemeier, D.P. Schneider & G.P. Garmire, A p J 580,L105 (2002). 21. L.C. Bassett, W.N. Brandt, D.P. Schneider, C. Vignali & G.P. Garmire, A J submitted (2004). 22. W.N. Brandt, A. Laor & B.J. Wills, A p J 528,637 (2000). 23. R. Maiolino, E. Oliva, F. Ghinassi, M. Pedani, F. Mannucci, R. Mujica & Y. Juarez, A&A 420,889 (2004). 24. X. Fan et al., ApJ 526,L57 (1999). 25. W.N. Brandt et al., in preparation.
1. 2. 3. 4. 5. 6.
A COMPOSITE EUV AGN SPECTRUM AND THE AGN CONTRIBUTION TO THE LOW REDSHIFT UV BACKGROUND
J. SCOTT AND G. KRISS STScI, 3700 San Martin Dr., Baltimore, MD, 21218 USA
M. BROTHERTON Univ. of Wyoming, Dept. of Physics and Astronomy, Laramie, W Y , 82071 USA R. GREEN KPNO/NOAO 950 North Cherry Avenue, Tucson, A Z 85726 USA
J. HUTCHINGS HIA/NRC, Victoria, BC V9E 2E7 Canada J. M. SHULL CASA, Dept. of Astrophysical and Planetary Sciences, Univ. of Colorado, Boulder, CO 80309 USA
W. ZHENG CAS, Dept. of Physics and Astronomy, JHU, Baltimore, MD 21218 USA
The Far Ultraviolet Spectroscopic Explorer ( F U S E ) has surveyed a large sample (> 100) of active galactic nuclei (AGN) in the low-redshift universe. Its response at short wavelengths makes it possible to measure directly the EUV spectral shape of QSOs and Seyfert 1 galaxies at z < 0.3. Using archival F U S E spectra, we form a composite extreme ultraviolet (EUV) spectrum of QSOs at z < 1 and compare it to UV/optical composite spectra of QSOs at higher redshift, particularly the composite spectrum from archival Hubble Space Telescope spectra. We use the F U S E composite spectrum to calculate the AGN contribution to the local ultraviolet background and find a value 70% larger than previous estimates.
291
292 1. Introduction
The ubiquity with which QSOs display spectral properties such as powerlaw continua and broad emission lines over wide ranges in luminosity and redshift has led to the use of composite spectra to study their global properties. Information about the continuum in the rest-frame ultraviolet is particularly critical for understanding the formation of the emission lines, for characterizing the Big Blue Bump, and for determining the ionization state of the intergalactic medium (IGM). Composite QSO spectra covering the rest-frame ultraviolet have been constructed for objects with 0.33 < z < 3.6 from HST [1,2(T02)]and at z > 2 from ground-based samples like the Large Bright Quasar Survey [3], the First Bright Quasar Survey [4], and Sloan Digital Sky Survey [5]. The FUSE bandpass, 905-1187 A, allows us to examine the EUV properties of local AGN. We can therefore study the same rest-frame wavelength region covered by the HST composite spectra at redshifts less than 0.33. The low redshifts of these AGN ensure that, although the FUSE aperture limits it to observing relatively bright AGN, our sample contains a large fraction of intrinsically low-luminosity objects. We use the FUSE composite to calculate the AGN contribution to the mean local ultraviolet background (UVB) . 2. FUSE Spectra and Composite Construction
Following T02, we excluded spectra of broad absorption line quasars and spectra with SIN < 1 over large portions from our FUSE sample. We also exclude spectra of objects that show strong narrow emission lines, strong stellar features, or strong interstellar molecular hydrogen absorption. A total of 128 spectra of 85 AGN meet the criteria for inclusion in the sample. We follow the same procedure as TO2 for the reduction of the sample spectra. To summarize: we correct for Galactic extinction using a standard extinction curve, individual E ( B - V) values for each AGN sightline, and Rv = 3.1; we ignore wavelength regions affected by ISM absorption lines; we correct for Lyman limit absorption if the S/N below the Lyman break is greater than one; we apply a statistical correction for the line of sight absorption in the Lya forest; we shift the AGN spectrum to the rest frame and resample to common 1 bins. Like T02, we describe the distribution of absorbers in redshift, z , and column density, N, by d 2 n / d z d N 0: (1 z)YN-O. We use ,6 = 2.0, for 12.2 < logN < 14.4 [6]. For 14.4 < logN < 16.7, we use ,6 = 1.35 [7],and
+
293 for the redshift distribution parameter, we use y = 0.15 [8]. We normalize the distribution by 1 . 3 4 ~ cm2 at log N = 13 and z = 0.17 and assume a Doppler parameter of 21 km s-l [6].
I ' ~ ~ ' 1 ' ~ ~ ~ 1 ' " ' 1 ' ' ' ' 1
HST Composite
-1
0
o
600
700
800
800
FUSE
m
+
1000
Rest-frame Wavelength (A)
Redshift
Figure 1. Top left: Composite AGN spectrum with power law continuum fit shown by dashed line and wavelength regions used in fit shown by solid line at bottom; H S T composite from TO2 shown for comparison. Bottom left: Ratio of FUSE t o H S T composite spectra. Right: Luminosity versus redshift for FUSE and H S T AGN.
We combine the sample spectra using the bootstrap technique described by T02. We fit a power law of the form F, o( ua to the continuum of the composite spectrum and find that the best-fit power law index is a = -0.56. This can be compared with the CXEUV for fits to wavelengths greater than 500 A in T02. We show the composite spectrum and its ratio to the HST composite in the left panels of Fig. 1. We find a standard deviation of 0.11 in a from 1000 bootstrap samples of the FUSE sample. This gives an estimate of the error arising from the range of spectral shapes of the individual AGN that constitute our sample. After exploring a number of other possible systematic errors, we find that the shape of the FUSE composite is most sensitive to uncertainties in the extinction correction and the column density distribution parameter, ,9. We estimate the total uncertainty, +0.38, -0.28, from different composites formed by varying these quantities. The EUV spectral index of the HST composite is significantly softer, a = -1.76 f 0.12. In the right panel of Fig. 1, we show the redshift and luminosity distributions of the FUSE and HST samples.
294
3. Summary We summarize our results as follows. (1) We construct a composite EUV (630-1155 A) AGN spectrum of objects with z < 0.67 from archival FUSE data. (2) We fit a power law continuum and Gaussian profiles to the emission lines in the composite spectrum, and we find that 0 VI/LY,Band Ne VIII emission are enhanced in the FUSE composite relative to the HST composite (Fig. 1). (3) We find that the best-fit spectral index of the composite is (Y = -0.56+0,:32:, where the estimate of the total uncertainty includes estimates of cosmic variance and various possible systematic errors. (4) The FUSE composite is harder than the EUV portion of the HST composite spectrum of T02, who find a = -1.76 f0.12 for 332 spectra of 184 AGN with z > 0.33. Since the FUSE sample has a larger fraction of lowluminosity AGN relative to the HST composite sample, we attribute the harder continuum and enhanced high-ionization emission lines to a manifestation of the Baldwin ef€tect [10,11,12]. (5) Finally, following the procedure outlined in previous work [13] we use the spectral shape of this composite t o quantify the AGN contribution to the local UVB. The spectral index of the FUSE AGN composite gives a higher UVB a t z 0 than that of the HST QSO composite [13] by a factor of 1.7. Given the uncertainties on current measurements of the local UVB from direct methods and from the proximity effect [14], this result is in agreement with them. N
References 1. W. Zheng et al., ApJ 475, 469 (1997). 2. R.C. Telfer et al., A p J 565, 773 (2002, T02). 3. P.J. Francis et al., ApJ373, 465 (1991). 4. M.S. Brotherton et al., ApJ 546, 775 (2001). 5. D.E. Vanden Berk et al., A p J 122, 549 (2001). 6. R. Dave & T.M. Tripp, A p J 553, 528 (2001). 7. S.V. Penton, J.M. Shull & J.T. Stocke, ApJ 544, 150 (2000). 8. R.J. Weymann et al., ApJ 506, 1 (1998). 9. D.J. Schlegel, D.P. Finkbeiner & M. Davis, ApJ 500, 525 (1998). 10. W. Zheng & M.A. Malkan, ApJ415, 517 (1993). 11. T.G. Wang et al., ApJ 493, 1 (1998). 12. M. Dietrich et al., A p J 581, 912 (2002). 13. J.M. Shull et al., A J 118, 1450 (1999). 14. J. Scott et al., ApJ 571, 665 (2002).
BL LAC X-RAY SPECTRA: SIMPLER THAN WE THOUGHT
E. s. P E R L M A N ~ ,T. DAUGHERTY~,A. KORATKAR~,G. MADEJSKI~,K. ANDERSSON2, J. H. KROLIK3, H. ALLER4, M. ALLER4, J. T. STOCKE5, T. RECTOR‘, P. PADOVAN17, A. MARSCHERs, M. ALLEN’ AND S. WAGNER~O
‘Joint Ctr for Astrophysics, University of Maryland-Baltimore County 2Stanford University, S L A C Dept. of Physics and Astronomy, Johns Hopkins University Department of Astronomy, University of Michigan Center f o r Astrophysics and Space Astronomy, University of Colorado ‘Department of Physics and Astronomy, University of Alaska - Anchorage European Southern Observatory ‘Department of Astronomy, Boston University Centre de Donnees astronomiques d e Strasbourg loLandessternwarte Heidelberg We report results from XMM-Newton observations of thirteen X-ray bright BL Lacertae objects, selected from the Einstein Slew Survey sample. The spectra are generally well fit by power-law models, with four objects having hard (a < 1;F, o( v P a ) spectra that indicates synchrotron peaks a t > 5 keV. None of our spectra show line features, indicating that soft X-ray absorption “notches” must be rare amongst BL Lacs, rather than common or ubiquitous as had previously been asserted. We find significant curvature in most of the spectra. This curvature is almost certainly intrinsic, as it appears nearly constant from 0.5 to 6 keV, an observation which is inconsistent with the small columns seen in these sources.
1. Introduction The nature of the X-ray emission and absorption from BL Lacs is still an open question. Most BL Lac objects have X-ray spectra that can be fit by power-laws within smaller bandpasses, such as that of ROSAT ([12],[17]) More recent results from ASCA [7] and BeppoSAX ([1],[11],[19]) have generally confirmed this spectral morphology, and also added onto it the possibility of intrinisic spectral curvature across a wider bandpass ([4],[6],[9],[16]). In addition, earlier missions had indicated that some BL Lac objects showed a deficit in soft X-rays below a power-law model, which had been interpreted 295
296 by invoking X-ray absorption features at 0.5-0.8 keV ([3],[8],[14],[15]). But not all bright BL Lacs were found to require such features (e.g., [5]). 2. Sample, Observations and Data Reduction
We selected our targets from the Einstein Slew Survey sample of BL Lacs [13]. The Slew Survey sample is the largest collection of X-ray bright BL Lacs, and was the first containing significant numbers of both HBLs and LBLs (high-energy and low-energy peaked BL Lacs; [18]).We received time for the 13 X-ray brightest objects (all HBLs) which were not on either XMM GTO lists or in the Cycle 1 Chandra schedule. Seventeen observations were done (four were repeated due to background flares). Because the main goal was to address the class properties, our integration times were short, 5 ks. As a result, the best data come from the EPIC instruments, which are imaging spectrographs that have low-to-moderate ( R 20 - 50) spectral resolution. All source and background extraction was done in SAS v5.4.1. X-ray spectral modeling was done in XSPEC v11.0. The PN data were fit between 1.1-10.0 keV, while the MOS data were fit between 0.5-10.0 keV, except for the faintest objects which we capped at 7.0 keV due to low count rates at the highest energies. Where multiple observations of an object were obtained, each observation was reduced and analyzed separately. Three models were fit: a single power law, sum of two power laws, and a logarithmic parabola. Each model was attempted with Galactic and variable absorption, and we also fitted several sub-bands t o investigate curvature. N
N
3. Results
The spectral indices we found range from r = 1.7 - 3.5, with 12/17 being in the range I? = 2.0 - 2.9. This is similar to previous findings. Four spectra were found to be flat (I' < 2). These objects are likely to have Vpeak > 5 keV. In 14/17 observations, a better fit was obtained by allowing for spectral curvature, which may be intrinsic, or the result of additional absorption. We believe the curvature is most likely intrinsic, because it appears nearly constant between 0.5-6 keV in all objects where it is required. This is inconsistent with absorption given the observed columns, which range from 3 - 20 x lo2' cm-2. The curvature can be characterized by &/d(log E ) M 0.4 f0.15. A similar curvature was found by Giommi et al. [4] for about 50% of X-ray bright BL Lacs observed by BeppoSAX. The greater percentage
297
Figure 1. Four examples of the curved X-ray spectra seen for the objects in our sample. All of these objects show steeper spectra at higher energies, with curvature that remains constant through at least 6 keV.
we find to require curvature, is consistent with the greater sensitivity of XMM. This type of curvature has more recently been analyzed ([9],[lO]) in the context of particle acceleration models, and given the multiple emission regions that most likely contribute to BL Lac X-ray spectra, a continuous curvature is the most likely result of spectral aging in several regions with different physical parameters (as opposed to the simpler model of a sharp cutoff, which is more commonly assumed). The finding of significant absorption features, stands in stark contrast to the claims of "ubiquitous absorption features" in the spectra of BL Lac objects, made by earlier workers. We are confident of this result based on the high signal-to-noise of these spectra. In addition, another, independent study of four of the five BL Lacs where BBXRT and ASCA spectra appeared to give these line features[2], found a similar lack of features. We believe the most consistent explanation for the earlier results is that those
298 spectra did indeed show curvature, similar t o what we see in our spectra, but interpreted t h a t curvature incorrectly as absorption.
References 1. V. Beckmann et al., A B A 383,410 (2002). 2. A.J. Blustin, M.J. Page & G. Branduardi-Raymont, A&A 417,61 (2004). 3. C.R. Canizares & J. Kruper, ApJL 278,L99 (1984). 4. P. Giommi et al., in Blazar Astrophysics with BeppoSAX and Other Observatories (Rome: ESA-ESRIN), ed. P. Giommi, E. Massaro & G. Palumbo, p63. (2002). 5. M. Guainazzi et al., A&A 342,124 (1999). 6. S. Inoue & F. Takahara, ApJ463,555 (1996). 7. H. Kubo et al., ApJ 504,693 (1998). 8. G. Madejski et al., ApJ 370,198 (1991). 9. E. Massaro et al., A&A 413,489 (2004). 10. E. Massaro et al., in Blazar Astrophysics with BeppoSAX and Other Observatories (Rome: ESA-ESRIN), ed. P. Giommi, E. Massaro & G. Palumbo, p3. (2002). 11. P. Padovani et al., MNRAS 328,931 (2001). 12. E.S. Perlman et al., ApJ 456,451 (1996a). 13. E.S. Perlman et al., ApJS 104,251 (199613). 14. R.M. Sambruna et al., ApJ 483,774 (1997). 15. R.M. Sambruna & R.F. Mushotzky, ApJ 502,630 (1998). 16. F. Tavecchio, L. Maraschi & G. Ghisellini, ApJ 508, 608 (1998). 17. C.M. Urry et al., ApJ 463,444 (1996). 18. C.M. Urry & P. Padovani, PASP 107,803 (1995). 19. A. Wolter et al., A&A 335,899 (1998).
SPECTRAL ENERGY DISTRIBUTION IN THE UV REGION OF TWO QUASARS *
- X RAY
S. A. R. HARO-CORZO, L. BINETTE, E. BENITEZ AND M. RODRIGUEZ-MARTINEZ Instituto de Astronomia- UNAM C. U. Circuit0 Exterior, C.P. 04510, Mexico E-mail:
[email protected] Y . KRONGOLD Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, M A 08138, USA E-mail: krongoldahead. cfa. harvard. edu
The aim of this contribution is to join together the UV spectra with the corresponding X ray spectra from Archived Data in public databases. We have been investigating the Spectral Energy Distribution of PKS 1354+195 and 3C334 combining HST-FOS and Chandra-ACIS/S data. These two Quasars were known to show a steepening of their SED near 1200 8, (quasar rest-frame).
1. Introduction
The spectral energy distribution (SED) of quasars between the Lyman limit and the soft X-rays (hereafter EUVX) is poorly constrained, the reason being that it cannot be observed directly as a result of the large photoelectric H I opacity of the Galaxy. Yet according to the prevalent photoionization theory, the emission lines observed in all Active Nuclei are the result of the reprocessing of this EUV into line emission. The ionizing energy distribution in the EUVX is therefore an essential ingredient to any proper model of the emission lines as well as to models of the w a r m absorbers that are observed in the soft X-rays or UV (a component intrinsic to the active nuclei). Fig. 1 (a) shows the gap in EUVX where is easy to *This work is supported by posgrado IA-UNAM and partially supported by CONACYT (F-40096).
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300
get a connection between the optical and X ray region defining the spectral index a ~ (2500A x to 2 keV).
Figure 1. (a) SED of Radio Loud Quasars from Elvis et al. (1994). (b) Composite Spectra in the UV region from Telfer et al. (2002).
In the work of Telfer et al. (2002, hereafter TE02), they used the HSTFOS data of 184 QSOs making a composite SED finding a steepening in the spectrum, which was described with a broken power law ( Fa 0: v + ~ ) Q -1.7 between 500-12OOA (see Fig. l(b)). Binette et al. (2003) showed the steepening can not be the result of absorption by the warm hot intergalactic medium, therefore most of the steepening must be intrinsic to Quasars, as initially proposed by TE02.
-
Our aim is to present preliminary results of the SED in the EUVX region of a subsample of QSOS from TE02, which showed the steepening near to 1200A and futhermore to join together with the X ray spectrum (Chandra ACE-S/NONE) available in public databases. The subsample is: PKS 1354+195 and 3C334. Both are Radio Loud Quasars and their principal parameters are listed in the Table 1. Table 1. Principal characteristics of the two quasars. name
Z
N H (cm-’)
extra-absorption
Photon Index
3c334 1354+195
0.555 0.718
4.210” [2] 2.181OZ0[4]
NO [l] NO [7]
-
N
-1.2 [I]
Variability NO [I] ~
7
1
2. Reduction
The CIAO’Sthreads were followed in order to get the X ray spectra of Chandra. The steps in session of CIAO 2.3 were: download the files evtl.fits, pcad-asoll.fits, fltl.fits, bpix.fits, aoffl.fits, soffl.fits. We deleted the file “ardlib.par” to begin a new reduction. The command “dmkeypar” give the
301
CCD active during the observation. From “dmkeypar” we obtained the relevant parameters such as the bad pixels, CALDB version, the pipeline version, the focal plane, temperature of the observation, the Exposure mode as TE or CC and the telemetry format as F, VF or G. We Apply the ACIS Corrections because our data are TE and VF and to convert the PHA to PI. However, we did not Clean ACIS BG in VF mode neither remove the acis-detect-afterglow correction, because the sources were pile-up. We apply an ACIS Gain Map, because the data were taken a t a temperature -120 degrees Celsius. We calculated the energy from the PHA channel and the Good Time Intervals with the command “dmcopy”. Now, to Remove the ACIS readout streak, we first found the physical position of the source and BG, using DS9 and saving the region with ciao format and physical coordinates as s.reg and bg.reg respectively. We checked if the data have subarray because the bg have to be rescaled with the factor x obtained with x=1024/(number of rows for the subarray). Once completed these steps, we are already to Create ACIS Spectra for Pointlike Sources and the bg with “dmextract”, but is necessary to locate the centroid (in meanchip coordinates) of the source and bg. The RMF file was calculated with “pset mkrmf” for the source and the bg, but before We need to create the aspect histogram, which is a binned representation of aspect motion during the observation using the Aspect Solution List Files. We need to know if there is a grating parameter in the observation using “dmkeypar”. In order to make the ARF file which gives the effective area vs. energy for a given observation and instrument configuration was used L‘punlearnmkarf” . We reduced the errors bars grouping the counts in bins with the command ” dmgroup” . The Next step was t o fit the spectra with Sherpa, where the best fit used (Q 0; x2 ) has Q = 1.
3. Summary
The results of the last session are resumed in the Table 2, in which we see that each quasar has different steepening (triangle line), it is clear in Fig. 2, however, that aox is around the typical range (dot line). The power laws in the X-ray region are represented with a solid line. In both cases, the extrapolation of the FUV-X power laws happened around l O I 7 Hz. For these two QSOs there are not a clear connection between the UV and X ray regions and apparently the steepening is intrinsic t o both quasars. We
302
3c334 2d.555 m
1354+19 L0.7
-10.5
I
E0 r(
I
0
0
-11
I UI bn
k
0,
v
2
-11.5
2 M
0
4
-12 15
16
17
18
1 0 1(Hz) ~
16
17
18
Figure 2. SED in the EUVX region of 3C334 (Left) and PKS 1354+195 (Right) .
need to improve the models (or to learn how to make new ones, see e.g. Sobolewska et al., Siemiginowska, and Steed et al., contributions in this volume) and to finish the analysis of the remaining observations of QSOs available in public databases. Table 2.
Principal results for the two quasars.
Q
-1.41
0.10
0.5
-1.27
-0.36
0.6
QNUV
~ F U V QOX
3c334
3.41OZ0
-0.69
-1.75
1354+195
3.01OZ0
-1.17
-1.73
References N. Jackson et al., A&A 274, 79 (1993). M. Elvis et al., AJ 97, 777 (1.989). M. Elvis et al., ApJS95, 1 (1994). J.K. Gambill et al., A&A 401,505 (2003). R.C. Telfer et al., A p J 565, 773 (2002). 6. L. Binette et al., A p J 590, 58 (2003). 7. F.N. Owen et al., A p J 250, 550 (1981).
1. 2. 3. 4. 5.
QX
N H (cm-2)
name
RADIO, FIR, OPTICAL AND X-RAY PROPERTIES OF NLSlS AND NLQSOS FROM THE SBS*
E. BENITEZ, I. CRUZ-GONZALEZ AND J. A. STEPANIAN~ Instituto de Astronomia UNAM, Apartado Postal 70-264, 04510 Mexico, DF Mexico E-mail:
[email protected] v. CHAVUSHYAN AND R. MUJICA~ Znstituto Nacional de Astrofisica, Optica y Electrdnica, Apartado Postal 512 y 216, Puebla, Puebla Mexico E-mail:
[email protected] In this work we summarize some of our main results on the multiwavelength p r o p erties of NLSl galaxies and NLQSOs isolated form the AGN sample of the Second Byurakan Survey (SBS). Our study shows that both samples share common p r o p erties such as: (1) strong soft-X ray emission, (2) most of them are radio-quiet objects, (3) most of them are weak FIR sources, (4) most are strong FeII emitters, FeII/Hp > 1. For the complete (i.e. B < 17.5) samples of NLSls and NLQSOs we found: (1) a linear correlation between L, and Lopi, (2) an anticorrelation between FeII/Hp vs. FWHM(Hp) which is related to the Eigenvector 1, and no correlation between ao3.and Lopt. Based on this results, we confirm that we are dealing with a single class of AGN NLSls/NLQSOs which includes low-and high-luminosity objects.
1. Introduction
A sample of 26 SBS NLSls that have -19.9 > M B > -23.0 and 0.0243 < z < 0.317 has been homogeneously selected in parallel with a sample of 25 SBS NLQSOs with -23.0 > M E > -25.5 and 0.15 < z < 0.63. In this contribution we point out that the mean parameters of SBS NLSls and NLQSOs are similar, except for the mean EW of Fe I1 of NLQSOs 'This work is based on data obtained at the GHO in Cananea, Sonora M6xico
t Work partially supported by grant ES118601 from DGAPA-UNAM. iWork partially supported by CONACYT grants 5-321783 and 39560-F
303
304
which is -1.4 times bigger than for NLSls. The optical, X-ray and radio luminosities of NLQSOs also have a wider interval. 2. Conclusions
A linear correlation between X-ray and optical luminosities was found1 for NLSls as well as an anti-correlation between FWHM(Hp) and FeIIX4570/Hp (related to Eigenvector 1). Both results are found again for the NLQSOs and strongly support the idea that SBS NLSls/NLQSOs may belong t o the same parent population. Taking both groups together the correlation becomes: log L, = 1.05 log L g - 2.7 (r=0.83). Contrary to previous results2 no correlation was found (r=O.ll) between ao, and logLopt for the 26 bright ( B 5 17.5 and z 50.16) SBS NLSls/NLQSOs:
a,, = 0.03 f0.13 log Lopt - 2.7 f 2.5.
(1)
Our study reveals that NLSls/NLQSOs are predominantly strong or moderately strong (< logLX >= 44.3) X-ray sources, although weak X-ray sources are found as well. They are mainly radio-quiet objects, only a few NLQSOs are radio-intermediate. None of the SBS NLQSOs were detected by IRAS. In the case of the SBS NLSls, one of our main findings was that almost all of them may not have the FIR bump, and their SED suggests that they may also possess the BBB3. The lack of detection of FIR emission in both samples could be due to flux detection limits of the IRAS survey. This suggests that SBS NLSls/NLQSOs are not ULIGs and that a significant number may not even be LIGs. So, these objects are predominantly weak FIR sources, where star formation and dust are not the dominant emission mechanisms. Finally, nearly 50% have Fe II4570/Hp > 1, i.e. they are strong FeII emitters. We have shown that SBS NLSls properties are also found in SBS NLQSOs4. NLQSOs are just the continuation to more luminous objects. We proposed that they should be called NLSl/NLQSO, which includes high-and low-luminosity objects. The SBS NLSl/NLQSOs sample of 51 objects deserves further investigation, specially in the IR, UV and X-rays. References 1. 2. 3. 4.
J.A. Stepanian et al., ApJ 588, 746 (2003). B. Wilkes, ASP Conf. Ser. 162,15 (1999). E. Benitez et al., RevMexAA SC 17,104 (2003). I. Cruz-GonzBlez et al., A&A submitted (2004).
FIRST RESULTS FROM A MULTI-WAVELENGTH SURVEY OF QUASAR JETS
J. M. GELBORD* MIT Center f o r Space Research, NE80-6091 77 Massachusetts Ave., Cambridge, MA 02139, USA E-mail:
[email protected]. edu
We present results based on the first 20 Chandra images obtained in a survey of jets in radio selected flat-spectrum quasars (FSRQs), along with new sub-arcsecond radio maps and optical images. We discover jet X-ray flux in 12 sources despite short exposures, establishing that FSRQ jets are often X-ray bright. The X-ray morphology typically matches the radio and fades rapidly after the first sharp radio bend, but there are notable exceptions. Optical non-detections rule out simple synchrotron models for jet X-ray emission, implying these systems are dominated by inverse Compton (IC) scattering. Models of IC scattering of the cosmic microwave background (CMB) constrain the bulk flow and magnetic field, suggesting the jets are oriented close to our line of sight, with deprojected lengths often >> 100 kpc.
We are conducting a survey of a large, flux-limited sample of FSRQs selected by extended 5 GHz flux (> 2” from the core). The 56 sample members span a wide range of radio morphologies and redshifts. Of these, 20 were observed by Chandra during cycle 3l. New sub-arcsecond resolution radio maps for all 20 were obtained with ATCA and VLA, and six (so far) have been imaged with Magellan2. Results are summarized in Table 1. X-ray jets are detected in 12/20 sources; a higher rate amongst the (radio) brighter jets suggests deeper X-ray observations would yield more detections. X-ray jets are one sided, with peaks usually coincident with radio knots up to the first sharp bend (Fig. 1). Low optical flux limits in five systems indicate that the synchrotron continua cut off below v 1014 Hz, suggesting that the X-ray flux is dominated by a different process. IC-CMB models3 fit best, suggest bulk Lorentz factors r-3-10 and magnetic fields Gauss, with jets directed within -20’ of our line of ~ i g h t l ? ~ .
-
*In collaboration with H.L. Marshall, D.A. Schwartz, D.M. Worrall, M. Birkinshaw, J. Lovell, D. Jauncey, E. Perlman, D. Murphy and R.A. Preston
305
Table 1. Some results for the 20 targets observed during Chandra cycle 3. Target name PKS 0208-512 PKS 0229+131 PKS 0413-210 PKS 0745+241 PKS 0858-771 PKS 0903-573 PKS 092S397 PKS 103CL-357 PKS 1046-409 PKS 1145-676 PKS 1202-262 PKS 1258-321 PKS 1343-601 PKS 1424-418 PKS 1655+077 PKS 1655-776 TXS 1828+487 PKS 2052-474 PKS 2101-490 PKS 2251+158
z
Bj mag
ADa
0.999 2.059 0.808 0.410 0.490 0.695 0.591 1.455 0.620
17.1 17.7 18.7 19.0 17.9 19.0 18.3 19.5 17.5 19.4 19.8 13.0 10.8f 18.0 18.8 17.5 17.1 18.2 17.1 16.6
B B A/B B B A/B A B A/B B A/B A A/B B B A A B B A/B
?e
0.789 0.017 0.013 1.522 0.621 0.094 0.692 1.489 ?e
0.859
Y N
Y N N
Y Y Y Y N Y Y Y N N N Y N Y Y
arx,jet
Sired
g2bbs
0.92 f .01 > 0.95 1 . 0 4 f .02 > 0.91 > 0.99 1 . 0 7 f .02 1 . 0 0 f .02 0.93 f .01 0.95 f .03 > 0.95 0 . 8 6 5 .01 1 . 0 3 f .03 1.01 f .02 > 0.91 > 0.88 > 1.07 0.91 f .01 > 0.89 0 . 9 9 f .02 0.955.01
23.4
>24.5
...
...
23.2
..'
... ...
...
> 26.0
22.9 23.4 23.0 24.5
>26.0 >25.5
...
22.5 23.7 23.3 " '
...
...
... ... >26.7
...
...
... ...
...
...
21.9
...
... 23.8 22.4
... >25.3
...
Note: a Membership in extended 5 GHz radio flux-limited (A) and/or morphologicallyIs jet detected in X-rays? ' g' mag predicted by synselected (B) subsamples. Observed jet limiting mag (no optical detections). chrotron model (using a,,,jet). 2 z to be measured with Magellan in 2004. f Gunn z mag; Bj extinction ~ 1 mag!
Figure 1. X-ray images with radio contour overlays for 092S397, 1202-262, 103S357 & 2101-490 (left to right). 0920 and 1202 are representative of most jet systems: the X-rays match the radio contours, fading rapidly after the sharp bend 5.6" NNW of the core of 1202. Uniquely, the X-rays in 1030 remain strong through a sequence of sharp bends. 2101 is unusual in that the X-ray knots lie between the radio peaks.
References 1. 2. 3. 4.
H. Marshall et al., A p J S submitted see http://space.mit.edu/Njonathan/jets. J. Gelbord et al., in prep. F. Tavecchio et al., ApJ 544, L23 (2000). D. Schwartz et al., New Astron. Rev. 47, 461 (2003).
THE X-RAY PROPERTIES OF THE P G QSO SAMPLE OBSERVED WITH XMM-NEWTON
E. JIMENEZ, E. PICONCELLI, M. GUAINAZZI AND N. SCHARTEL XMM-Newton Science Operations Center, RSSD of ESA, Apd 50727, 28080-MADRID SPAIN We present preliminary results of a systematic analysis of the XMM-Newton spectra of nearby optically bright QSOs. The objects have been selected from the Bright Quasar Survey sample. The goal of this project is to characterise the X-ray spectral properties of optically selected QSOs in the 0.3-12 keV energy band. In most cases, two component continua are sufficient to model reasonably well the observed spectra. All but one detected Fe KCYline have narrow profiles.
1. Preliminary results of the analysis of the XMM-Newton
P G QSO sample The sample consists of 30 QSOs observed by XMM-Newton, and selected from the Bright Quasar Survey, (MB erg/s) and very little data exist on the spectral properties of lowluminosity AGNs (Lbol < lo4’ erg/s). We selected a complete sample of Seyfert galaxies from the Palomar optical spectroscopic survey of nearby galaxies for which a comprehensive and homogeneous catalog of spectral classifications have been produced (Ho et al. 1997). The sample selected (composed by 60 Seyfert galaxies) is complete down to B ~ = 1 2 . 0mag and it covers a large range of AGN luminosities, i.e. L2-10keV erg/s. Recently, multi-wavelength surveys from the radio to the infrared band have been performed on sub-samples of the Ho et al. (1997) sample of Seyfert galaxies. Taking advantage of these extensive data set, it is thus possible to consider here the highest quality nuclear fluxes and therefore assemble the SEDs from radio (v M 10’ Hz) to hard X-rays (v E lo1’ Hz)
-
309
310
I
10
15
log u (Hz)
20
10
,
,
,
15
,
20
log u (Hz)
Figure 1. Individual SEDs, separated vertically by arbitrary constants for clarity. The galaxy name is shown on the left of each SED. Left panel: Seyfert 1’s. Right panel: Seyfert 2’s.
for a significant fraction of the objects in our sample. The best quality individual SEDs of type 1 and type 2 Seyfert galaxies are presented in Figure 1, shifted vertically by arbitrary constants, for clarity. The data from the radio to the hard X-rays have been drawn as filled dots. A comparison of the average spectral properties of the two classes of Seyferts shows that: (i) in both cases the far and mid infrared emission appear to dominate the energy output, (ii) the near infrared, optical and X-ray emission up to 10 keV are significantly different in the two classes, type 2 objects showing lower luminosities. The results obtained are in agreement with Seyfert unified models predictions in which Seyfert 2s are the obscured version of Seyfert Is. The complementation of those spectral windows poorly covered such as the UV band and the interpretation of the nuclear SED along with different accretion models will be the subjects of a future work.
References 1. L.C. Ho, A.V. Filippenko & W.L.W. Sargent, ApJS 112,315 (1997).
SEARCH FOR RADIO QUIET BL LACERTAE OBJECTS
T. PURSIMO Nordic Optical Telescope, Sta Cmz de La Palma, E-38700 Tenerife, SPAIN
T. RECTOR University of Alaska Anchorage, A K 99508 USA M. TORNIKOSKI Metsahovi Radio Observatory FIN-0.2540 Kylmala, Finland D. LONDISH Dept. of Astrophysics University of Sydney N S W 2006, Australia We present the first results of radio and near infrared observations of a sample of objects discovered by the 2dF QSO redshift survey. This sample has 56 objects which exhibit a featureless optical continuum, a steep number-magnitude relation and lack detectable proper motions suggesting they are extragalactic and likely BL Lac objects. However, contrary to the vast majority of BL Lac these objects are not detected from radio or X-ray surveys. Based on our deep radio follow up observations many objects are fainter than 0.1 mJy at centimetre and 0.3 Jy at millimetre region. The optical-NIR photometry suggests that some objects have non-thermal continuum similar to BL Lacertae objects however some objects have a black body spectrum suggesting galactic DC white dwarf origin.
1. Introduction BL Lacertae objects are a class of active galactic nuclei (AGN), that are characterized by rapid variability from radio through TeV energies, high and variable optical polarization and apparent superluminal motions in their VLBI-radio structures. Many observations of BL Lacs indicate that this emission is dominated by beamed flux from a relativistic jet, oriented close to our line of sight (e.g. Urry & Padovani 1995). Based on unification schemes of radio loud AGN, BL Lacs are thought to be FR I radio galaxies, seen along the jet axis. 31 1
3
BL Lacs are relatively rare and most BL Lac discoveries have been made using radio and X-ray surveys. Recently Londish (2003) presented the BL Lac sample which is extracted from the 2QZ spectroscopic survey. These 45 optically relatively faint objects with a featureless optical continuum have no detected proper motion and a steep number-magnitude relation, which is similar to that of the 2QZ QSOs. However, unlike many BL Lac objects at radio and X-ray wavelengths, these objects are very faint. Only eight objects have been detected in NVSS, FIRST or ROSAT surveys. The centimetre follow-up observations of 24 objects were made a t the VLA (D-array) a t 8.4 GHz in 2003. In the millimetre region we made observations of 26 objects, with the Metsahovi Radio Telescope in Finland a t 37 GHz, and of 15 objects with the Swedish-ESO Submillimetre Telescope (SEST) in Chile a t 90 GHz. The near infrared observations of 6 objects were carried out a t the Nordic Optical Telescope (NOT) in April 2003. 2. Results
All six objects observed a t NOT have also been observed using the VLA. However, only two objects were detected, with flux densities of 0.1 and 0.33 mJy at 8.4 GHz. Using non simultaneous measurements of the optical brightness (Londish 2003), the radio-optical spectral indices of these two objects are 0.08 and 0.17, somewhat smaller values than those of a typical BL Lac object or "radio loud" AGN. The remaining six objects have s s . 4 1) and large stellar masses imply that they would be matured galaxies with vigorous star formation at very high redshifts.
1. AGN candidates in the ISOISSA13 field A 23 hour exposure using the Japanese Guaranteed Time has revealed 33 significant mid-infrared sources (detection S/N > 4.3, equivalent to a total flux of 12 pJy) with the ISOCAM LW2 filter (5-8.5 pm) in a 5' x 5' area in the Hawaii Deep Field SSA 13.4 This field has been observed with SCUBA (850 pml), Chandra (2-10keV2), and VLA/FIRST (1.4cm7). As we have already reported mid-infrared and submillimeter associations in Sato et al. 20023, here we focus on the X-ray and radio sources. There are four Chandra sources and one VLA/FIRST source in the ISOCAM coverage. Each of these is very near to a particular 6.7pm source.' This gives us an upper limit of 15 % AGN contribution to faint 6.7pm sources down to 12 pJy. 2. Multiwavelength properties of the AGN candidates
Fig. 1 shows that optical to submillimeter parts of the SEDs are well above power laws derived from X-ray and radio flux levels. None of the five AGN candidates shows a stellar profile at B-, I - , and K-bands. Assuming AGN 31 3
314
contributions are negligible except at the X-rays and radio, we deduced photometric redshifts using a SED model GRASIL.6
-
4
- 2 0 2 4 Lag (Wavelength [pm])
6
-
4
- 2 0 2 4 Lag (Wavelength [pm])
6
-
4
- 2 0 2 4 Lag (Wavelength [pm])
-1
-3
z&.l6
Arp220
-5
-
4
- 2 0 2 4 Log (Wavelength [pm])
6
-
4
- 2 0 2 4 Lag (Wavelength [pm])
6
Figure 1. X-ray to radio spectral energy distributions (SEDs) of the five AGN candidates5 Axis ranges are fixed.
3. Nature of the AGN candidates Comparing with other 6.7pm galaxies, the AGN candidates are red in the optical, faint even at the infrared bands, located at high redshifts ( z > l), and have large stellar masses which were evaluated directly from their restframe near-infrared light. All these suggest t hat X-ray and radio phenomenon are likely t o be related with the formation of large stellar systems at very high redshifts. References 1. A.J. Barger, L.L. Cowie, D.B. Sanders, E. Fulton, Y . Taniguchi, Y. Sato, K. Kawara & H. Okuda, Nature 394, 248 (1998). 2. R.F. Mushotzky, A.J. Barger, L.L. Cowie & K.A.Arnaud, Nature 404, 459 (2000).
3. Y. Sato, L.L. Cowie, K. Kawara, Y. Taniguchi, Y. Sofue, H. Matsuhara & H. Okuda, ApJ 578, L23 (2002). 4. Y. Sato et al., A @ A 405, 833 (2003). 5. Y. Sat0 et al., A J 127,1285 (2004). 6. L. Silva, G.L. Granato, A. Bressan & L. Danese, ApJ 509, 103 (1998). 7. R.L. White, R.H. Becker, D.J. Helfand & M. D. Gregg, ApJ 475, 479 (1997).
6
Luminosity Functions, Evolution and Contribution to the Cosmic Background
31 6
Andrea Comastri and Adelita
X-RAY LUMINOSITY FUNCTIONS OF ACTIVE GALACTIC NUCLEI
T. MIYAJI Physics Department, Carnegie Mellon University 5000 Forbes Ave., Pittsburgh, PA 15213, USA E-mail: miyaji@cmu. edu
In this proceedings paper, I overview the current status of the X-ray luminosity function of AGNs in the soft (0.5-2 keV) band, extended using XMM-Newton and Chandra survey data. We found that the number density of low luminosity AGNs peaks later in the history of the universe ( z 1) than that of high luminosity AGNs ( z 1.7 - 3). I also describe the basic results of a spectroscopic followup project of a complete HEAO-1 hard X-ray limited sample of AGNs using ASCA and XMM-Newton and present separate intrinsic hard X-ray luminosity functions for unabsorbed and absorbed AGNs. We found that the absorbed AGN XLF drops more rapidly at high luminosities, indicating a deficiency of absorbed luminous AGNs. N
N
1. Introduction
X-ray surveys are practically the most efficient means of finding active galactic nuclei (AGNs) over a wide range of luminosity and redshift. In order to construct an X-ray luminosity function (XLF) of AGNs, enormous efforts have been made to follow up X-ray sources with optical telescopes to establish their nature as AGNs and t o measure their redshifts. Now we have fairly complete samples of X-ray selected AGNs over 6 orders of magnitude in flux, from surveys ranging from all the high galactic latitude sky to the deepest pencil-beam fields. These enable us t o construct and probe luminosity functions over cosmological timescales. In this proceedings article, I overview the current progress of a few projects related t o AGN XLF. Firstly, I overview the results of the soft X-ray (0.5-2 keV) luminosity function (SXLF) , which is the continuation of our previous work with ROSAT samples", extended with deep X M M Newton and Chandra surveys. While the soft X-ray surveys select against obscured AGNs, in the current situation, the number of available objects and area-flux coverage from 317
318
extensive surveys make them useful for probing detailed behaviors of XLFs of the unabsorbed portion of the AGN activity. A complementary XLF in the hard band (2-10 keV) (HXLF) enables us to also look into obscured AGNs, and thus it provides most direct measure of the accretion onto supermassive blackholes (SMBHs). Ueda et al. in this volume covers our extensive recent work on HXLF (see also Ueda a t al. 200320 for a full description). In this article, we also present the results of our XMM-Newton and ASCA spectroscopic follow-up of a complete hard X-ray flux-limited sample of bright AGNs selected from HEAO-1 catalogslg, the basic results of which have been integrated in the Ueda et 81’s HXLF. 2. AGN Soft X-ray Luminosity Function and Evolution 2.1. The Combined Sample
In addition t o the ROSATsamples used in our previous work11i12,we have added AGNs from the ROSAT North Ecliptic Pole Survey (NEPS)‘, from an XMM-Newton observation on the Lockman Hole and the Chandra Deep Surveys South17/North2. For the Lockman Hole region, the inner part based on the ROSAT HRI has been replaced by a new XMMNewton sample’. Four medium-deep ROSAT surveys used in our previous work11i12,i.e., the UK Deep Surveyg, Marano Fieldz2,North Ecliptic Pole (deep P S P C - p ~ i n t i n g )and ~ the outer part of the Lockman Hole (PSPC)15 are now collectively called the ROSAT Medium-Sensitivity Survey (RMS). The combined area versus limiting flux relation and the redshift-luminosity diagram are shown in Fig. 1. The samples are summarized in Table 1. We have tried to limit our analysis t o “type 1” AGNs (including narrowline Seyfert 1 galaxies). In the ROSAT samples, we selected type 1 AGNs mainly from the optical classifications. For the XMM-Newton Lockman Hole and Chandra DEEP field samples, the optical classification is supplemented by hardness ratios of the X-ray sources. AGNs with z < 0.015 have been excluded from the analysis to avoid the possible effects of the local large scale structure. Details will be explained in Hasinger et al. (in preparation).
’
2.2. SXLF and Evolution with Redshij?
The soft X-ray Luminosity functions (SXLF) in different redshift bins have been calculated using the Nobs/Nmdlestimator, where each redshift bin
319 F' ."".', .'"" . Survey Area
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Figure 1. Left: The survey area of the combined soft X-ray sample as Table 1. The Soft X-ray Sample Survey
NAGN
Area [deg21 2 . lo4
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[cgsl M 250
203
Area [deg21 RMS9i22>15 1.-0.5
SA-Nl
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has been maximum-likelihood fitted with a smoothed two power-law form and the model value at the center of each bin is multiplied by the ratio of the actual number of AGNs in the bin to the model-predicted number12. Nominally, corrections for incompleteness due to unidentified X-ray sources have been made by using an effective survey area, derived by multiplying the geometrical survey area by the completeness of the survey (i.e. identified fraction of the detected X-ray sources). This method is vaIid when sources remain unidentified because of random reasons that are not correlated with the intrinsic properties of the source (e.g. optical magnitude). This is not necessarily true, especially in the deepest surveys. Thus we also calculated the XLF or number density upper bounds, where all the unidentified XMM-Newton and Chandra sources are assigned (in duplicate) the central redshift of each bin. Figure 2 (left) shows the SXLF in different redshift bins (plotted only the nominal incompleteness correction case). Figure 2 (right) shows the AGN number densities as a function of red-
320
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,'Opt., MB ~the . high X-ray lumiluminous ( M B < -26) QSO number d e n ~ i t y l ~In nosity bin, we are not still certain (within the uncertainties in the incompleteness correction) whether we have detected the decline (with z ) in the number density a t z > 2.7, where the densities of luminous optical 14,5 and radioi8 QSOs clearly show a drop. Note, however, that when we take a different method on incompleteness correction involving optical magnitude limits with our soft X-ray sample, a density decline a t z > 2.7 is preferred even for the high-luminosity sample (Hasinger et al. in preparation).
-
321 3. The Brightest Hard X-ray Sample
24
23.5
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23 22.5
20.5
20
Figure 3. Left: The local de-absorbed HXLF (2-10 keV) of unabsorbed (Log N H cm-2 5 21.5; filled circle) and absorbed (> 21.5; filled triangle) AGNs. The open squares show the sum of both. Right: Intrinsic absorption of the sample AGNs are plotted against the intrinsic (de-absorbed) luminosity. There would be N 9 objects in the region enclosed by a thick dashed line if absorbed and unabsorbed AGNs intrinsic HXLFs were the same besides normalizations.
In order to construct the luminosity function of AGNs in the intrinsic X-ray luminosity, X-ray surveys in the hard band ( E > 2 keV) and X-ray spectroscopic (or at least hardness) information are crucial. In order to complement deeper ASCA, XMM-Newton and Chandra surveys with smaller survey areas, we have defined a bright hard X-ray selected sample from the HEAO-1 all-sky surveys. In addition to the famous Piccinotti et al.13 sample from the HEAO-1 A2 experiment, we have defined a somewhat deeper hard X-ray flux-limited sample of AGNs from the MC-LASS catalog of X-ray sources from the HEAO-1 A1/A3 experiments a in a limited region. The AGN sample from the latter catalog was investigated in detail by Grossan7. As a total, 49 AGNs are defined and we have made spectral analysis of all of them (except one) using ASCA and XMM-Newton observation from archive as well as our own proposals. We have determined the intrinsic absorption N H and underlying power-law index r. This enabled us to construct separate local HXLFs for absorbed and unabsorbed AGNs as functions of de-absorbed (intrinsic) luminosity (Fig. 3, left). We see that a http://heasarc.gsfc.nasa.gov/docs/heaol/archive/heaol_catalog. html
322 the absorbed AGN HXLF drops more rapidly than the unabsorbed one a t high luminosities. This can also be demonstrated in the L, - NH plot (Fig. 3, right). Suppose absorbed and unabsorbed AGNs had the same HXLF shape, there would be N 9 AGNs in the region enclosed by a thick dashed line in this figure. See Shinozaki et a1.I’. Full results will be reported by Shinozaki et al. (in preparation).
Acknowledgments I thank my collaborators on the projects described in this article, especially Giinther Hasinger, Maarten Schmidt, Keisuke Shinozaki, Yoshitaka Ishisaki and Yoshihiro Ueda. I thank the conference organizers for the invitation t o give a talk. This work has been supported by the NASA LTSA grant NAG5-10875.
References 1. I. Appenzeller et al., A & A 364,443 (2000). 2. A. Barger et al., A J 126,632 (2003). 3. R.G. Bower et al., M N R A S 281,59 (1996). 4. T. Di Matteo et al., ApJ 593,56 (2003). 5. X. Fan et al., A J 121,54 (2001). 6. I.M. Gioia et al., ApJS 149,29 (2003). 7. B. Grossan, PhD Thesis, MIT (1992). 8. V. Mainieri et al., A & A 393,425 (2002). 9. I.M. McHardy et al., M N R A S 295,641 (1998). 10. K.O. Mason et al., M N R A S 311,456 (2000). 11. T. Miyaji, G. Hasinger & M. Schmidt, A & A 353,25 (2000). 12. T. Miyaji, G. Hasinger & M. Schmidt, A & A 369,49 (2001). 13. G. Piccinotti et al., ApJ 253,485 (1982). 14. M. Schmidt, D.P. Schneider & J. Gunn, A J 110,68 (1995). 15. M. Schmidt et al., A & A 329,495 (1998). 16. A. Schwope et al., A N 321,1 (2000). 17. G.P. Szokoly et al., ApJS submitted (2004). (astreph/O312324) 18. P.A. Shaver et al., Nature 384,439 (1996). 19. K. Shinozaki et al., in Stellar-Mass, Intermediate-Masss, and Supermassive Black Holes, in press (2004). (astro-ph/0402363) 20. Y . Ueda, M. Akiyama, K. Ohta & T. Miyaji, ApJ, 598,886 (2003). 21. J.S.B. Wyithe & A. Loeb, ApJ 595,614 (2003). 22. G. Zamorani et al., A & A 346,731 (1999).
THE MISSING X-RAY BACKGROUND
A. COMASTRI INAF-Osservatorio Astronomico d i Bologna, via Ranzani 1, I-40127 Bologna, Italy E-mail: andrea.
[email protected] The fraction of the hard X-ray background (XW) resolved into individual sources by the deep Chandm and XMM-Newton surveys strongly depends on the adopted energy range and decreases with increasing energy. As a consequence the nature of the sources of the even harder (> 10 keV) X R B remains observationally poorly constrained. I will briefly discuss the need for X-ray observations above 10 keV.
1. Introduction
After the impressive achievements obtained by Chandra and XMM-Newton in terms of angular resolution and high energy throughput, almost all the papers dealing with X-ray observations of extragalactic sources begin with the following general statement: ... Deep Chandra and XMM-Newton surveys have resolved most of the X R B into discrete sources... While there are no doubts about the origin of the XRB, the above statement is true only when referred to the 2-10 keV energy range and it is even more true around 2-3 keV rather than above 7-8 keV, where the resolved fraction is no more than 50%22. At energies greater than 10 keV, where the bulk of the XRB energy density is produced, the resolved fraction is negligible, being strongly limited by the lack of imaging X-ray observations at high energies. As far as the 10-100 keV band is concerned, we are currently facing the problem already encountered for the 2-10 keV band right after a significant fraction of the 1 keV background was resolved by Einstein' surveys. The most important difference is that a solid model for the XRB, based on the AGN unification scheme, is now available. First proposed by Setti and Woltjer" and elaborated with an increasing level of details since that time'3~3~9 the XRB synthesis is obtained assuming a dominant contribution of obscured AGN with a wide range of column densities and luminosities. Though differing in several details regarding the luminosity function and X-ray spectral shape parameterization, the different flavours of synthesis 323
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E [keV] Figure 1. A selection of XRB spectral measurements collected from observations with different satellites as labeled. ROSAT blue7; BeppoSAX greenz1; XMM-Newton magenta” and yellow5; RXTE cyan15; HEAO1-A2 blacklo and HEAOl-A4 LED greenlo; HEAO1A4 MED redll. Also reported is the integrated contribution of resolved sources in the Chandra CDFSlg (gold points) and in XMM-Newton Lockman holez2 (red bow-tie). The solid magenta curve represents the analytical fit of Gruber 1992 renormalized upward = 400 keV) by 30% in order to fit the most recent measurements. The blue (ECZLt = 100 keV) solid curves represent the integrated contribution of the and red (ECZLt model described in the text. The short-dashed curves correspond to unabsorbed AGN (logNH < 22 cm-’), while the long-dashed curves correspond to obscured Comptonthin sources (22 < logNH < 24 cm-’). See astro-ph/0406031 for the colored figure.
models, published so far, share the same key feature: the X-ray obscuration. In the following I will refer to these as absorption models. Massive campaigns of multiwavelength follow-up observations have made possible to obtain spectroscopic and photometric redshifts for several hundreds of hard X-ray (2-10 keV) selected Chandra and XMM-Newton source^^^^^ (see Tables 1 and 2 in Brandt et aL2 for a summary). The discovery of a sizable fraction of X-ray obscured sources agrees, at least to a first approximation, with the absorption models predictions. However the observed absorption and redshift distributions are poorly reproduced by current models.
325 Although a rather obvious way to cope with these problems is to construct absorption models with different luminosity and absorption functions until a better agreement with the overall observational constraints is achieved (see for instance Ueda et a1.20), a relatively large region of the parameter space remains unaccessible due to the lack of observational constraints. Within the framework of absorption models, the shape of the XRB spectrum and intensity in the 10-100 keV range, where most of its energy density is contained, is modeled assuming an important contribution from heavily obscured Compton thick ( N H > 1.5 x cm-2) sources around 20-30 keV. Moreover a high energy cut-off (E,,t) usually parameterized as an exponential roll-over with an e-folding energy of the order of a few hundreds of keV has to be present in the high energy spectrum of all the sources in order not to overproduce the observed XRB above 100 keV. The most reliable observational constraints on the Compton thick AGN space density and the exponential cut-off energy have been obtained thanks to the PDS instrument on board BeppoSAX . Though limited to bright 10100 keV fluxes, the BeppoSAXresults indicate that a fraction as high as 50% of the Seyfert 2 galaxies in the nearby Universe are obscured by Compton thick gas16, while the e-folding energy in the exponential cut-off spans a range from about 80 to more than 300 keVI4. In the following I will briefly discuss the impact that different assumptions on the fraction of Compton thick sources and Ecut values of the continuum have on the synthesis of the high energy XRB spectrum. Given that the emission processes reponsible of Compton thick absorption and high energy cut-off are basically driven by Compton scattering, I will refer to this approach as Compton models.
2. Resolved and Unresoved XRB For the purposes of the present exercise I will adopt the parameters used by Comastri et al. (1995). Although there are compelling evidences which indicate that the evolution of the X-ray luminosity function could not be parameterized by pure luminosity evolution anymore simple as postulated in the simplest versions of absorption models,20 it is important to point out that the most recent findings are not expected to substantially modify the model predictions above 10 keV. The starting and admittely extreme assumption is that Compton thick absorption is not energetically relevant. Since the observational constraints
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E [keV] Figure 2. The residual background spectrum after subtraction from the two models reported in Fig. 1 (red line for E,,t = 100 keV, blue line for Ecut = 400 keV). Data as in Figure 1. The HEAOl-A4 LED dataset (green points in Fig. 1) are not reported for clarity. See astro-ph/0406031 for the colored figure).
on the presence of Compton thick sources beyond the local Universe are rather poor and only a few examples have been reported (see Comastri4 for a review), hereafter I will consider only the effects of two representative values (100 and 400 keV) for the high energy cut-off. It is possible to account for the resolved fraction of the 1-10 keV background as measured by Chandra citetozzi and XMM-Newton citeworsley with an appropriate, but reasonable, tuning of the absorption distribution. More specifically the ratio between Compton thin and unabsorbed AGN (assuming logNH < 22 as the dividing line) is in the range 2.0-2.4 (for E,,t=400 and 100 keV respectively) to be compared with 2.8 in the absorption model of Comastri et al. (1995). The resulting model spectra are reported in Fig. 1 along with a compilation of XRB data which clearly demonstrates a mismatch between the first HEAOl-A2 measurement and the recent estimates in the 2-10 keV band. The maximum de-
327 viation is of the order of 40% a t 10 keV. For the purposes of the present discussion I consider the analytical fit of Gruber (1992) renormalized upward by a factor 1.3 and slightly modified above about 60 keV t o match the HEAOl-A4 MED spectrum. This approximation results in a quite good description of the 2-10 keV XMM-Newton data and settles in between BeppoSAX and RossCXTE observations. Though the renormalized Gruber analytical fit provides a reasonable description of the broad band XRB spectrum a few words of caution are appropriate. A closer look a t the XRB data points above the peak indicates, besides cross-calibration uncertainties between the A4 LED/MED experiments, a sharp break a t E > 40 keV which is responsible for the knee in the analytical approximation. Moreover while it is obvious that the peak in the XRB spectrum must be around a few tens of keV, the exact location and intensity may still be subject to significant uncertainties, especially after the recent measurements below 10 keV which cast doubts on the normalization of the HEAOl-A2 data. The residual spectra (Fig. 2), computed subtracting the model predictions from the renormalized “observed” XRB intensity, are subjected to the caveats illustrated above.
3. Conclusions Not surprisingly, the shape of the model dependent residual background is reminiscent of that of extremely obscured sources. While the contribution of a yet uncovered population of high redshift Compton thick sources‘ may contribute to fill the gap, it is interesting to note that the residual spectrum peaks a t energies of the order of 30-50 keV (depending upon the assumed ECut).If the peak is associated to a characteristic energy in the source spectra, then for a typical redshift of N 1 this would correspond to 60-100 keV rest-frame. These energies cannot be obtained by increasing absorption because a t high column densities Compton down-scattering strongly depresses the entire high energy spectrum. An alternative possibility implies high energy cut-off values clustered within a relatively narrow range which in turns depends on the average redshift (E,,t 50-100 keV for ( z ) N 1) of the sources. Such a population has to be relatively well localized in space in order t o reproduce the rather sharp spectral break of the residual spectrum (especially pronounced if ECut= 400 keV, blue curve in Fig. 2) which otherwise would be smeared out integrating over the cosmological volume. Taking a t the face value the results above described it is also possible that the sources of the residual background are characterized by a truly N
328
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1.1-1.2) up t o several tens of keV which breaks t o a much steeper (I' N 2.6-2.9) slope (not necessary an exponential cut-off) at higher energies. Although it seems premature t o invoke a new population of sources with a peculiar hard X-ray spectrum the present exercise highlights the need for X-ray observations in the E > 10 keV domain.
Acknowledgments I kindly acknowledge support by INAOE, Mexico, during the 2003 Guillermo-Haro Workshop where part of this work was performed. Partial support from AS1 I/R/057/02 and MIUR Cofin-03-02-23 grants is also acknowledged. Giancarlo Setti, Gianni Zamorani and Cristian Vignali are acknowledged for a careful reading of the manuscripts and illuminating comments. A special thank t o Raul P.M. Mujica and Roberto P. Maiolino for organizing a stimulating and exciting workshop and for their patience.
References 1. A.J. Barger et al., AJ 126,632 (2003). 2. W.N. Brandt et al., in Physics of Active Galactic Nuclei at All Scales, eds. D. Alloin, R. Johnson & P. Lira (Springer-Verlag, Berlin), (2004). (astroph/0403646) 3. A. Comastri, G. Setti, G. Zamorani & G. Hasinger, A&A 296,1 (1995). 4. A. Comastri, in Supermassive Black Holes i n the Distant Universe, Ed. A. J. Barger, Kluwer Academic, (2004). (astro-ph/0403693) 5 . A. De Luca & S. Molendi, A&A 419,837 (2004). 6. A.C. Fabian, R.J. Wilman & C.S. Crawford, MNRAS 329,L18 (2002). 7. I. Georgantopoulos et al., MNRAS 280,276 (1996). 8. R. Giacconi et al., ApJ 234,L1 (1979). 9. R. Gilli, M. Salvati & G. Hasinger, A&A 366,407 (2001). 10. D.E. Gruber, in The X-ray background, Eds. X. Barcons, A.C. Fabian, Cambridge University Press, p. 44 (1992). 11. R.L. Kinzer et al., & L.E. Peterson, ApJ 475,361 (1997). 12. D.H. Lumb, R.S. Warwick, M. Page & A. De Luca, A&A 389,93 (2002). 13. P. Madau, G. Ghisellini & A.C. Fabian, MNRAS 270,L17 (1994). 14. G.C. Perola et al., A&A 389,802 (2002). 15. M. Revnivtsev et al., A&A 411,329 (2003). 16. G. Risaliti, R. Maiolino & M. Salvati ApJ 522,157 (1999) 17. G.P. Szokoly et al., ApJS submitted, (2004). (astro-ph/0403693) 18. G. Setti & L. Woltjer A&A 224,L21 (1989). 19. P. Tozzi et al., ApJ 562,42 (2001). 20. Y . Ueda, M. Akiyama, K. Otha & T. Miyaji ApJ 598,886 (2003). 21. A. Vecchi et al., A&A 349,L73 (1999). 22. M.A. Worsley et al., MNRAS in press (2004). (astro-ph/0404273)
ACTIVE GALACTIC NUCLEI IN THE MID-IR. EVOLUTION AND CONTRIBUTION TO THE COSMIC INFRAREDBACKGROUND
F. LA FRANCA AND I. MATUTE*+ Dipartimento di Fisica, Universitci R o m a D e V i a della Vasca Navale 84, I-00146, Roma, ITALY E-mail: lafrancaQfis.uniroma9.it,matuteQmpe.mpg.de
We present the first measure of the evolution of type 1 and 2 active galactic nuclei (AGN1 and AGN2) in the mid-infrared (15 pm). We used a sample of 52 AGN selected from the southern ELAIS fields combined with a local sample of 91 AGN from the IRAS Faint Source Catalog. We find that AGNI follow a luminosity dependent luminosity evolution with a rate k ~ = 2 . 6 ,which stops at z larger than 2. A similar evolutionary scenario is found for AGNZ with k~=2.0-2.6,depending on the adopted k-correction. We estimate that AGNl contribute about 3% to the cosmic mid-infrared background, while the AGN2 contribution is about 10%.
1. Introduction
Dust infrared emission has been observed in all active galactic nuclei (AGN). At least in the near and mid-infrared (MIR), it has been recognized that a not negligible fraction of the dust radiation is due to the heating of the AGN. For this reason it has been argued that AGN may contribute significantly also to the cosmic infra-red background (CIRB). This issue is of utmost importance, since it would also have implications on the fraction of the CIRB which should be ascribed to star formation. In this paper we investigate the evolution and contribution of AGN to the CIRB by using the most recent optical spectroscopy identifications (La Fkanca et al. 2004; Pozzi et al. 2003) of the 15 pm sources of the southern fields of the European Large Area Survey (ELAIS)a. The evolution of the *Present address: Max-Planck Institut fur extraterrestrische Physik (MPE) Garching bei Munchen, Germany +Other people involved: F. Pozzi, C. Gruppioni, C. Lari, G. Zamorani aData and related papers about the ELAIS southern survey are available at: http://www.fis.uniro1na3.it/NELAIS-S
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Figure 1. Left: MIR SED of AGNl from Elvis et al. (1994),NGC1068 and Circinus (top), and the derived k-corrections (bottom). Right: AGN used to compute the LF in the L15-z space. All the AGN present in the RMS catalog are plotted, while only sources with f 1 Z p n > 300 mJy were used for the estimate of the LF.
star-forming galaxies has been investigated by Pozzi et al. (2004), while a first estimate of the luminosity function (LF) of AGNl can be found in Matute et al. (2002). The final estimate on the evolution of the AGN in the MIR and their contribution to the CIRB is published by Matute et al. (2004). We assumed Ho = 75 Km s-l Mpc-l, Rx = 0.7 and R, = 0.3. 2. Samples
The MIR selected AGN samples used in this work have been extracted from the 15pm southern hemisphere ELAIS samples S1 (Lari et al. 2001; Gruppioni et al. 2002; La F'ranca et al. 2004) and S2 (Pozzi et al., 2003) and the local 12pm sample of Rush, Malkan and Spinoglio (1993, RMS). ELAIS is the largest single open time project conducted by I S 0 (Oliver et al. 2000; Rowan-Robinson et al. 2004), mapping an area of -12 deg2 at 15pm and 90pm. Five main fields were observed: N1, N2, N3 in the northern hemisphere, and S1 and S2 in the south. The S1 sample covers -4 deg2 down to 0.5 mJy at 15pm. We have restricted our analysis to a reliable subsample of 406 sources. The spectroscopic identification of -75% of these sources down to R-21.5, the completeness function of the areas, as well as the observed counts for each class of sources (Starburst galaxies and AGN) are presented by La F'ranca et al. (2004). S2 is a smaller area covering 0.12 deg2 and includes 43 sources at 50 down to 0.4 mJy (Pozzi et al. 2003).
-
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331 Classification of AGNl was done selecting all sources with broad emission line (FWHM>1000 Km/s). AGN2 were classified following classic diagnostic diagrams (e.g. Veilleux & Osterbrock 1987). In total the southern ELAIS (Sl+S2) AGN sample consists of 27 AGNl and 25 AGN2. We have combined our data with a local sample of AGN observed by IRAS (RMS). We selected only sources with f1zPm 2 300 mJy, leaving us with 41 AGNl and 50 AGN2. 3. The evolution of AGN
Luminosities (vL,) were computed in the MIR (15pm), and the optical (R band), assuming typical Spectral Energy Distributions (SED). For AGNl we used the compilation of Elvis et al. (1994) and the k-correction by Natali et al. (1998), in the MIR and R-band respectively. In clear contrast to AGNl, MIR SEDs of AGN2 vary greatly from starburst-type SED like Circinus, showing prominent emission from PAH molecules and deep absorption a t -1Opm, to more power-like SED, dominated by hot dust directly heated by the active nucleus, as in NGC1068. For this reason we used both SED as representative of two extreme cases of obscured AGN. Figure 1 shows the distributions in the L15 - z plane of the total sample of sources used in this analysis. The adopted shape of the LF is a 2 power law of the form: -da(L15) -
dlogLl5
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+ (L15/L;5)’
We assumed a luminosity evolution of the form: L15(z) = &,(0)(1+ z ) ~ ~ . A dependency with z was introduced in the form of: a(.) = aaexp(ab/z)+ a,. The parameters for the luminosity function and the evolution have been derived using an un-binned, maximum likelihood method as described by Matute et al. (2002). A factor O ( z , L ) ,was introduced in order to take into account of the limits of the spectroscopic identifications in the ELAIS samples. This factor is computed taking into account the observed ratio and spread between the infrared and optical luminosities of AGNl and AGN2. The function to be minimized can be written as:
where R(z,L) is the effective area coverage of each subsample. The goodness of the fits has been verified with the bi-dimensional Kolmogorov-Smirnov
332
Figure 2. Left: Type 1 AGN local (z=O.l) and high-z (2=1.2) 15pm LF. Right: Redshift distribution of AGN1. Gray and white areas represents the ELAIS and RMS sources respectively. Lines are predictions from the best fit taking into account the limits of each survey: dotted-dashed for RMS, dashed for ELAIS, while continuous is for total.
test (2DKS). The normalization factor a* is found in order to reproduce the observed total number of sources (ELAIS RMS). In order to compute the LF of AGNl we covered the z-L space from z=O to z=4 and from logL15=42 to logL15=47. In total 68 AGNl were used. In figure 2 is shown the observed space density distribution and the best fit model for two redshift intervals, z=[0,0.2] where the RMS sources dominate and z=[0.2,2.2] mainly populated by ELAIS. The optical completeness factor, R(z, L ) , was computed taking into account the relation: log(LlS/LR) = 1.45, where luminosities are expressed in solar units, with an intrinsic la dispersion of 0.25. This relation implies that ~4 AGNl (13% of the ELAIS sample) are expected to be missed because they are test ( f l a ) for AGNl fainter than the spectroscopic limits. The V/V,,, (0.61 f0.06) gives a clear indication of evolution. The amount of evolution found from our best fit, lc~=2.4-2.6,with a redshift cut-off zcut=2.0, is similar to what is already known at other wavelengths like the optical and X-ray, where the value for this evolution is found to be between 2 and 3. The 2DKS probability is 0.32. In order to compute the LF of AGN2 a total of 75 sources were used. The optical completeness factor, R(z, L), was computed taking into account the relation: 10g(L15/LR) = 0.4710gL15 - 5.02, with an intrinsic la dispersion of 0.32 (see La Franca et al. 2004). This relation implies that ~ 1 0 % of the AGN2 from the ELAIS sample are expected to be missed because they are fainter than the spectroscopic limits. The evolution was computed between z=O and z=0.7. The LF of AGN2 is found to be similar to the LF of AGN1, not only in the faint and bright slopes but also in the amount of evolution
+
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Figure 3. Left: Observed and fitted LF for type 2 AGN at z=O.05 ( t o p ) and z=0.35 (bottom). The luminosity was computed using the NGC-1068 MIR k-correction. At high redshift, a thin line represents the fit to the low redshift sources. Right: Observed and predicted redshift distribution of AGN2. Symbols are as in Figure 2.
with kL ranging from 2.0 to 2.6, if the NGC1068 or the Circinus SED are used, respectively. A flattening of the faint slope of the LF with increasing z is also present in the AGN2 (see Fig. 3). The 2DKS probabilities of the fits are larger than 0.3.
4. Discussion and conclusions
The best-fit models of the LF of AGNl and AGN2 provide also a good fit to the observed integral counts (Figure 4). According to our fits, integrating up to z = 3.5 and assuming a redshift cutoff of the luminosity evolution of the AGN2 equal to the one of the AGNl (zCut=2.0),we predict a total contribution of AGN to the CIRB of 10-12%. This value should be corrected for two opposing factors. Our estimate include the contribution of the AGN host galaxies. Silva et al. (2004), starting from the X-ray luminosity function and NH distribution of AGN predict that genuine nuclear activity contributes less that 5% to the CIRB, while the simultaneous starburst activity of the host galaxies contribute 10-20%. The second, opposite factor, is that, according to our preliminary analysis of 100 Ksec long XMM-Newton observations of part of ELAIS-S1, we expect that about 10% of the spectroscopically classified starburst galaxies harbor an AGN2 (La
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Franca et al. in prep). This is not surprising as recent X-ray surveys have revealed significant numbers of (mostly absorbed) AGN whose optical spect r a do not show signs of AGN activity (see e.g. Fiore et al. 2000). This could be partly due t o the dilution with increasing z of the AGN2-like optical spectra by the light of the hosting galaxy entering the slit (see e.g. Moran et al. 2002). A definite estimate of the MIR AGN evolution and contribution to the CIRB requires both deep MIR and X-ray observations of significantly large areas of sky such as those provided by the next coming observations of the XMM-Newton fields in the ELAIS-S1 region by Spitzer within the framework of the SWIRE survey (Lonsdale 2003).
References 1. M. Elvis et al., ApJS 95, 1 (1994). 2. F. Fiore et al., New Ast. 5 , 143 (2000). 3. C. Gruppioni et al., MNRAS 335, 831 (2002). 4. F. La Franca et al., A J in press (2004). (astro-ph/0403211) 5. C. Lari et al., MNRAS 325, 1173 (2001). 6. C. Lonsdale et al., PASP 115, 897 (2003). 7. I. Matute et al., MNRAS 332, L11 (2002). 8. I. Matute et al., in preparation (2004). 9. F. Natali, E. Giallongo, S. Cristiani & F. La Franca, AJ 115, 397 (1998). 10. E.C. Moran, A.V. Filippenko & R. Chornock, A p J 579, 71 (2002). 11. S. Oliver et al., MNRAS316, 749 (2000). 12. F. Pozzi et al., MNRAS 343, 1148 (2002). 13. F. Pozzi et al., A p J in press (2004). (astro-ph/0403242) 14. M. Rowan-Robinson et al., MNRAS in press (2004). (astro-ph/0308283) 15. B. Rush, M.A. Malkan & L. Spinoglio, ApJS 89, 1 (1993). 16. L. Silva et al., MNRAS submitted (2004). (astro-ph/0403381) 17. S. Veilleux & D.E. Osterbrock, ApJS 63, 295 (1987).
BRIDGING THE COSMIC INFRARED BACKGROUND TO THE X-RAY BACKGROUND
L. SILVA INAF-TFieste, Via Tiepolo 11, I-34131 fiieste, Italy
R. MAIOLINO INAF-Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy G. L. GRANATO INAF-Padova, Via Osservatorio 5, I-35122 Padova, Italy We have estimated the contribution of AGN and of their host galaxies to the IR background and source counts. Our ingredients are: the luminosity function and evolution of AGN recently determined by the hard X-ray surveys, and new X-ray to IR spectral energy distributions (SED) for AGNs as a function of their absorption column density N H . We find that AGN contribute < 5% over most of the IR range, whereas galaxies hosting AGNs contribute 10 - 20% in the 1 - 20pm 5% at X < 60pm. These results are obtained by relying mostly on range, and observed quantities, with only minor assumptions. N
N
1. Introduction
AGNs are known to be the main contributors of the X-ray background (XBG). Both, synthesis models,6 and direct observations with XMM and Chand~-a,~ have shown that the XBG is due to a mixture of obscured and unobscured AGNs. The surveys have revealed a different evolutionary pattern for low (Seyfert like) and high (QSO like) luminosity AGN, the former showing a redshift peak lower ( z < 0.5) than the latter. Since the circumnuclear gas responsible for the X-ray absorption is associated with dust that absorbs the UV-optical radiation from the AGN and reprocesses it in the IR, part of the IR background (IRBG) is due to AGN rather than star formation. A reliable quantification of the relative amount provided by the two processes is of fundamental importance to put constraints also for galaxy formation and evolution. We have investigated the contribution of AGN to the IRBG and IR source counts by making use of the most recent
335
336 hard X-ray luminosity function (LF) and evolution by Ueda et a1.,16 and new and accurately derived X-ray to IR SEDs for AGN and for their host galaxies, as a function of N H . 2. Spectral Energy Distributions
Nuclear SEDs: From a sample mainly taken from Maiolino & Rieke,12 those Seyfert nuclei with enough nuclear data in the mid to far-IR, and also in the X-ray band (to infer their intrinsic X-ray flux and N H ) have been selected. The photometric points have been interpolated and extrapolated with the Granato & Danese7 model for dusty tori. The SEDs have been normalized to the intrinsic X-ray flux and averaged within different N H bins. For QSOs, since essentially no nuclear data are available, and anyway only for unobscured QSOs, the same shape of the SEDs as that of Seys has been adopted. The IR/X normalization has been observationally determined by selecting QSOs from various sample^.^^^^^^^^ Total SEDs for AGN and their hosts: The SEDs of the host galaxies of AGNs have been determined as a function of the Lx of the nuclei, by collecting NIR to FIR data that include all the galaxy. By subtracting the SEDs of the nuclei, the residuals have been fitted with galaxy models, normalized to the intrinsic X-ray flux and averaged within bins of Lx. 3. Results
Coupling the hard X-ray LF by Ueda et a1.,16 perfectly reproducing the available constraints on the XBG, X-ray counts and redshift distributions, with the SEDs for AGN, we have estimated the contribution of AGN (nuclear and combined with their hosts) to the IR bands. In Fig. 1 we show our estimated contribution of AGN nuclei and combined with their hosts to the IRBG. Also shown in the plot is the contribution by galaxies (including spheroids and late-types) as described in Silva et al.14 While we find that the energy provided by AGN nuclei is a small fraction (- 3 to 5% between 5 and 40 pm), that due to galaxies associated with AGNs is significant (> 5% at all wavelengths < 40pm, and a few percent even in the sub-mm). In Fig. 2 we compare with the 15pm counts. We find that the AGN IR emission contributes significantly (- 10 - 30%) to the number counts at bright fluxes in several near and mid-IR bands, with the MIR ones being dominated by heavily obscured AGNs. When the hosts are included, their
337
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Figure 1. The IR background. Thin continuous line: total AGN; dotted: QSOl; dashed: QS02; dotted with signs: Seyl; dashed with signs: Sey2; dot-dashed: galaxies; thick continuous: total. Data by Hauser & Dwek (2001). Left: contributions by nuclear AGNs. host galaxies. The thick crosses show the estimated Right: contributions by AGNs contribution at 15pm for type 1 AGN by Matute et al. (2002), and for total AGN by Fadda et al. (2002).
+
+
+
contribution is always found to be > 10% at all X < 100pm at bright fluxes. We have worked out also predictions for the contribution of AGNs to the Spitzer bands. For X 5 24pm we expect that important fractions of the total detected sources will be provided by AGNs, while only a few percent at the longer bands. 4. Conclusions
We have estimated the contribution of AGNs to the IRBG and IR source counts, by using the most recent LF and evolution from the hard X-ray surveys,16 and new detailed SEDs for AGN. We find that AGN contribute little to the IRBG (< 5%), but their host galaxies provide a significant contribution ( N 5 - 20% at X < 60). AGN are an important fraction of the MIR sources at bright fluxes, and galaxies hosting an AGN probably dominate the MIR counts at fluxes > 1mJy. These results are derived by using mostly observed quantities with only minor assumptions. More details are given in Silva, Maiolino, & Granato (2004). The AGN SEDs are available at http://www. arcetri. astro.it/Nmaiolino/agnsed.
Acknowledgments We thank INAOE for financial support and kind hospitality.
338 6
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Figure 2. The 15pm integral counts. Line coding as in Fig. 1. Left: contributions by host galaxies. Data by Elbaz et al. nuclear AGNs. Right: contributions by AGNs (1999), Gruppioni et al. (2002).
+
References 1. P. Andreani, A. Franceschini & G.L. Granato, MNRAS 306, 161 (1999). 2. P. Andreani et al., AJ 125, 444 (2003). 3. D. Elbaz et al., A B A 351, 37 (1999). 4. D. Fadda et al., A&A 383, 838 (2002). 5. R. Giacconi et al., ApJ 551, 624 (2001). 6. R. Gilli, M. Salvati & G. Hasinger, A B A 366, 407 (2001). 7. G.L. Granato & L. Danese, MNRAS 268, 235 (1994). 8. C. Gruppioni et al., MNRAS 335, 831 (2002). 9. M. Haas et al., A B A 354, 453 (2000). 10. M. Haas et al., A B A 402, 87 (2003). 11. M.G. Hauser & E. Dwek, ARABA 39, 249 (2001). 12. R. Maiolino & G.H. Rieke, ApJ 454, 95 (1995). 13. I. Matute et al., MNRAS 332, L11 (2002). 14. L. Silva et al., A B A submitted, (astro-ph/0403166) (2004). 15. L. Silva, R. Maiolino & G.L. Granato, MNRAS submitted, (astroph/0403381) (2004). 16. Y . Ueda, M. Akiyama, K. Ohta & T. Miyaji, ApJ 598, 886 (2003).
COSMOLOGICAL EVOLUTION OF THE HARD X-RAY AGN LUMINOSITY FUNCTION
Y. UEDA Institute of Space and Astronautical Science, Sagamihara, 229-851 0, Japan M. AKIYAMA Subaru Telescope, National Astronomical Observatorg of Japan, Halo, HI 96'720 K. OHTA Department of Astronomy, Kyoto University, Kyoto, 606-8502, Japan T. MIYAJI Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213 We investigate the cosmological evolution of the hard X-ray luminosity function (HXLF) of Active Galactic Nuclei (AGN) in the 2-10 keV luminosity range of 1041.5 - 1046.5erg s-l as a function of redshift up to 3, utilizing a highly complete sample consisting of 247 hard X-ray selected AGNs. We find that (i) the fraction of X-ray absorbed AGNs decreases with the intrinsic luminosity and (ii) the evolution of the HXLF of the whole AGNs is best described with a luminosity dependent density evolution where the cutoff redshift increases with the luminosity. Our results directly constrain the evolution of AGNs that produce a major part of the hard X-ray background (XRB), thus solving its origin quantitatively. Based on these results, we discuss the growth history of supermassive black holes (SMBHs) in galactic centers.
1. Introduction
To reveal the cosmological evolution of the AGN luminosity function has been a main goal of X-ray surveys. In this paper we investigate the evolution of AGNs that constitute a major part of the 2-10 keV X-ray background, from a hard X-ray selected sample with an extremely high degree of completeness covering the wide flux range from lowloto 3.8 x erg cmP2 s-'. The full description is given in Ueda et al. (2003; hereafter U03) l . Finally, we present the growth curve of SMBHs traced by our HXLF and compare the results with a local black hole mass density in local universe. We adopt the cosmological parameters of ( H o , R,, R,) = (70h70 km s-l Mpc-l, 0.3, 0.7). For recent work of related subjects, see Refs. 2-5. 339
340 2. Luminosity Dependence of the Absorbed-AGN Fraction Figure l(a) shows the averaged absorbed-AGN fraction derived in three luminosity ranges at all redshifts. Figure l(b) shows its redshift dependence derived from the sample of 43 < Log Lx< 44.5 ( L x is the rest-frame 2-10 keV luminosity before absorption throughout the paper). No significant redshift dependence is evident from the data. Our result indicates that simple extension of the “unified scheme” to higher luminosity where the fraction of absorbed AGNs is assumed to be constant needs to be modified. This effect is taken into account in the population synthesis model by U03.
z
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0.3
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\
42
44
46
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0
1
2
Redshif t
3
Figure 1. The fraction of absorbed AGNs with Log NH > 22 to all AGNs with Log N H < 24, given as as a function of (left :a) luminosity and (right :b) redshift. The data points in (b) are calculated from AGNs in the luminosity range of Log L X = 43-44.5. Dashed lines represent the best fit model of the N H function.
3. The Hard X-ray AGN Luminosity Function
We find that a luminosity-dependent density evolution (LDDE) model, where the cutoff redshift above which the density evolution terminates increases with the luminosity, well describes the cosmological evolution of the HXLF. Figure 2 shows the comoving spatial density of the whole (type I plus 11) Compton-thin AGNs as a function of redshift integrated in three luminosity regions. 4. The Growth History of SMBHs
The HXLF gives firm observational constraints on the growth history of SMBHs through accretion process. The evolution of total accreted mass density, p ( z ) , is related to the HXLF as
341 LO-'
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'
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where
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Figure 2. The comoving spatial density of AGNs as a function of redshift in the luminosity range of Log Lx =41.5-43 (upper), 43-44.5 (middle), 44.5-48 (lower). The lines are calculated from the best-fit model of the HXLF. The error are lo, while the long arrows denote the 90% upper limits (corresponding t o 2.3 objects). The short arrow (marked with a filled square) corresponds to the 90% upper limit on the average spatial density of AGNs with Log Lx =43-44.5 at z=1.2-2.3 when all the unidentified sources are assumed to be in this redshift bin.
is the mass-to-energy conversion factor and i(z) =
J
Lbol@(LX, z ) a o g L X
(2)
is the comoving bolometric luminosity density. The comparison of p(0) with the local SMBH mass density estimated from the demography of galaxies can be used to constrain E . It is important that we should refer to a luminosity function of all the AGNs including type-I1 objects, otherwise p ( z ) would be significantly underestimated. In previous studies6-8, the authors estimated p(0) from the hard XRB intensity assuming a single effective redshift for the XRB sources. Now we have observationally determined the HXLF, which enables us to obtain p ( z ) more accurately by integrating the formula (1). To calculate A, an X-ray luminosity must be converted t o a bolometric one, Lbol. This correction is an issue, however, because the spectral energy distribution of AGNs depends on the luminosity and because complicated selection effects would be present. Here we assume the relation L X cx LE9 between the 2-10 keV and B-band luminosities, based on the results from a large, X-ray selected sample '. Then, we consider two simplified cases: the bolometric luminosity is proportional to the B-band luminosity, Lbol = 1 1 . 8 v ~ L ~ 4[ =. 51045(&&)1/0.9] ~ (case I), where UB is the B-band frequency, and to the 2-10 keV luminosity, Lbol = 3OLx (case 11). These correction factors are based on the mean spectrum of quasars complied by Elvis et al. (1994) lo. The difference between the two cases may give an estimate for the uncertainty due to the bolometric correction. The results of i ( z ) and p ( z ) are plotted in Figure 3 (thick lines for case I and thin lines for case 11). We extrapolate our HXLF model to the range
342 of z=3-5 and calculate p ( z ) assuming E = 0.1 and z,, = 5 (i.e., p(5) = 0). Since our HXLF contains only Compton-thin AGNs, we also show the results by dashed lines when 1.6 times as many Compton-thick AGNs as those with Log N H = 23-24 are included (with no redshift dependence). Compared with the results of p(z) by Yu & Tremaine (2002) where the optical luminosity function of type-1 quasars12 is utilized, we find a significant growth of the SMBH after z < 1 owning to contribution of absorbed, low luminosity AGNs. We obtain the estimated total accreted mass density of p(0) = (2.2 - 5.3) x lo5 MOMpcV3, in agreement of a recent estimate of the SMBH mass density of (3.2 - 6.5) x lo5 M ~ M ~ C - ~ by Marconi et al. (2004)13. This indicates that accretion with E _N 0.1 is the major process for the growth of SMBHs. More detailed discussion can be found in Marconi et al. (2004), supporting this conclusion.
4 ~
~
5-
, ,
c 4
Figure 3. Upper panel: the growth curve of SMBHs traced by the HXLF (total accreted mass density as a function of redshift). The mass-to-energy conversion factor E = 0.1 is assumed. Lower panel: evolution of the comov-
ing bolometric luminosity density for LX > 1041.5erg s-l. The HXLF model is extrapolated to the range of z > 3. Solid line: only . Compton-thin AGNs are considered. Dashed : line: Compton-thick AGNs are included. The bolometric correction is made assuming Lbol = 1 1 . 8 L ~0: L;”” (case I: thick lines) and Lbol = 6 3OLx (case 11: thin lines).
i
0
1
2
3
z
4
References 1. Y . Ueda et al., ApJ 598, 886 (2003, U03). 2. L.L. Cowie et al., ApJ 584, L57 (2003). 3 . G. Hasinger, AIP Conf. Proc. 666, 227 (2003). 4. F. Fiore et al., A&A 409, 79 (2003). 5. A.T. Steffen et al., ApJ596, L23 (2003). 6. P. Salluci et al., MNRAS 307, 637 (1999). 7. A.C. Fabian & K . Iwasawa, MNRAS 303, L34 (1999). 8. M. Elvis, G. Risaliti & G. Zamorani, A p J 565, L75 (2002). 9. S. F. Anderson et al., A J 126, 2209 (2003). 10. M. Elvis et al., ApJS 95, 1 (1994). 11. Q. Yu & S. Tremaine, MNRAS 335, 965 (2002). 12. B.J. Boyle et al., MNRAS 317, 1014 (2000). 13. A. Marconi et al., MNRAS in press (2004).
CENSORS: THE VLT/VLA MJY SOURCE SURVEY FOR HIGH REDSHIFT AGN EVOLUTION
M. H. BROOKES AND P. N. BEST Institute for Astronomy, Blackford Hill, Edinburgh,
EH9 3HJ, UK E-mail:
[email protected],
[email protected] The Combined EIS-NVSS Survey Of Radio Sources (CENSORS) has been produced with the primary goal of investigating the cosmological evolution of the radio luminosity function. This 1.4GHz sample, complete to the 7.2mJy level, contains 150 radio sources. Host galaxies are almost entirely identified in optical and near-IR bands and the sample is now approaching 70% spectroscopic completeness. We show preliminary results demonstrating how CENSORS will improve upon previous work and how it is applicable to other projects.
1. Introduction Radio galaxies and radio loud quasars are among the most powerful objects in the Universe. Observable at high redshifts, they trace large scale structure and are associated with the most massive black holes[l], they therefore have great potential for revealing the evolution of massive galaxies and investigating the relation between active galactic nuclei (AGN) and galaxy formation. However there are still many questions facing radio-loud AGN astrophysicists. For example, the high redshift cosmological evolution of strongly radio active sources is a property that has not been resolved and so provides a route by which we may gain a better understanding of these objects. This is of far-reaching importance: given their association with the most massive black holes, we would also learn about the evolution of the upper part of the black hole mass distribution. In 1990 Dunlop and Peacock[2] undertook a study of cosmic evolution of the radio luminosity function (RLF) presenting the first evidence of a decline in the comoving number density of powerful radio sources beyond z 2.5 (the redshift cut-off). Since then numerous advances have provided
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343
344
a good consensus in the determination of the low redshift RLF (eg.[3]), but the high redshift evolution and the reality of the redshift cut-off in the radio source population remain areas of controversy. For example, the deep sample of Waddington et a1.[4] shows evidence of a cut-off in number density of low luminosity sources beyond z > 2, but has insufficient sky coverage to investigate the most luminous sources. Conversely, the sample of Jarvis et a1.[5] proved too shallow to resolve the issue. Shaver et al.[6] claimed evidence for a sharp decline in number density of flat spectrum sources between z 2.5 and z 5. However Jarvis and Rawlings[7]showed that this result was erroneous due to a failure to properly account for the spectral index of the sources. So high redshift RLF evolution of radio sources remains ill-understood.
-
-
Figure 1. This plot, based upon the pure luminosity evolution models of Dunlop and Peacock (1990), demonstrates that a 1.4GHz radio survey with flux limit just below lOmJy will maximise the information on high redshift powerful radio sources.
2. CENSORS
Controversy in earlier work begins at z -2.5, so CENSORS was designed to maximise information at these redshifts (see Figure 1). CENSORS contains all the NVSS sources above 7.2mJy that are within the ESO Imaging Survey (EIS) Patch D (2 x 3 degrees; 09 51 36 - 21 00 00). High resolution VLA imaging of CENSORS allowed EIS I band imaging (I 5 23) to be used to identify host galaxies using a maximum likelihood method analysis[8]. Remaining sources have been identified using K band imaging using UKIRT, the AAT and the VLT[9]. Following spectroscopy, at the
345
VLT, the ESO 3.6m and the AAT[10], the sample is also now approaching 70% spectroscopic completeness with further follow-up on-going. 3. Results
Given the current status of CENSORS we may establish its potential to build upon previous work using the spectroscopic redshifts where we have them, and estimated reshifts using the K-z and I-z relations where we do not. For example, the additional coverage it offers in the radio luminosity vs. redshift plane is illustrated by Figure 2. By plotting the estimated Radio Luminosity YS, Redshift l ~ t ' " " " " " ' ' ' ' ' " " ~ ' " ' " ' , ' ' ' ' " " ~ ,
3 Redshift
Figure 2. This P-zplane shows how adding CENSORS to samples like 3C, 6C and 7C will help t o break the radio luminosity-redshift degeneracy.
redshift distribution (Figure 3) we demonstrate that CENSORS improves upon the predictions of Dunlop and Peacock, as some of their allowed fits clearly depart from the CENSORS distribution. Hence, we are probing information which was not included in the former investigation. We also test for CENSORS. In the highest redshift bin show a banded falls well below 0.5. Although the error bars here do not account for the estimation in the redshift distribution, this gives tentative indications of negative evolution at high redshift. To clarify the high redshift evolution we intend to use this sample, in conjunction with others, such as 3CRR[11],BLR[12] and the Parkes selected regions[l3],to model the evolution of the RLF. Not only will we improve on previous work by our choice of sample but, in cases where a spectroscopic redshift has not yet been obtained, we will model target redshifts with a
&
2
346 photometric redshift probablitiy distribution. We will, therefore, be able to account for this uncertainty within the model and in the reliability of the results. Banded
T e ~ for l CENSORS
0.8
t Figure 3. Left:The redshift distribution of the CENSORS sample compared with the model predictions of Dunlop and Peacock 1990. FF indicates the free form models.Right: A banded test for CENSORS, shows negative evolution at the highest redshifts.
&
4. Further Investigations
CENSORS will also be useful in other important investigations. For example the nature of the K-z relation for radio galaxies and its dependence on radio luminosity, the comparison of evolution of radio loud and quiet sources and the dependence of sources properties on environment.
References 1. J.S. Dunlop et al., M N R A S 340,1095 (2003). 2. J.S. Dunlop & J.A. Peacock, M N R A S 247,19 (1990). 3. B. Mobasher et al, M N R A S 308,45 (1999). 4. I. Waddington et al., M N R A S 328,882 (2001). 5. M.J. Jarvis et al., M N R A S 327,907 (2001). 6. P.A. Shaver et al., Nature 384,439 (1996). 7. M.J. Jarvis & S. Rawlings, M N R A S 319,121 (2000). 8. P.N. Best et al., M N R A S 346,627 (2003). 9. M.H. Brookes et al., in prep, (2004a). 10. M.H. Brookes et al., in prep, (2004b). 11. R.A. Laing et al., M N R A S 204,151 (1983). 12. P.N. Best et al., M N R A S 310,223 (1999). 13. A.J.B. Downes et al., M N R A S 218,31 (1986).
10 YEARS OF BL LAC SELECTION: WHAT HAVE WE LEARNT?
M.J.M.
MARCHA*
CAAUL, Observatdrio Astrondmico de Lisboa Tapada da Ajuda 1349-018 Lisboa Portugal E-mail:
[email protected] In the past 10 years there has been a proliferation of surveys with the objective of selecting a wider range of the BL Lac population. The result is that indeed the number of BL Lacs now known is considerably larger, however, some of the questions raised by the first BL Lac samples are still hovering over us. It is therefore important to review what we have learnt from the recent efforts of selecting larger and deeper samples of BL Lacs, and try to understand what are the necessary lines of investigation.
1. Introduction The past ten years have seen a significant increase in the number of BL Lacs known due primarily to the effort of selecting deeper and larger samples of these type of radio-loud AGN. In fact, until 1991 only two statistically well defined samples of BL Lacs existed: one selected in the radio - the 1 Jy sample' - and another selected in the X-rays - the EMSS sample.2 The analysis of these two samples which contained less than 40 sources each, yielded different statistical properties for the radio and X-ray selected sources. Perhaps the most striking one, and the most difficult to understand, was the difference in the deduced cosmological evolution in both samples. Whereas in the case of the radio selected sample the BL Lacs showed positive or no evolution, in the case of the X-ray selected sources, the analysis yielded strong negative evolution. The search for the reason of such puzzling result had at least two significant repercussions: it empha*Work supported by the Portuguese Fundqfia para a Cidncia e Tecnologia through the grant POCTI (SFRH/BPD/3610/2000) and the project PESO/P/PR0/1254/98).
347
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sised the need for deeper and larger samples of BL Lacs, and the need to quantify possible selection effects introducing different biases in the samples. Because BL Lacs are thought to live in the core of bright ellipticals, without deeper samples we only ever get to see the most extreme cases of the phenomenon where the AGN overwhelmingly outshines its host, thus making it difficult to investigate the relationship between the two. On the other hand, without proper quantification of the selection effects that play a role in each sample, the view we achieve is one where intrinsic properties are masked by ‘artificial’ relationships introduced during the selection process.
2. Selection effects
The task of obtaining deeper and larger samples was taken up by different groups. At present there are a variety of samples selected at both radio and X-ray frequencies (see for instance Refs. 3, 4, 5, 6) which are sure to increase our understanding of the BL Lac population as a whole. Most of these samples have adopted a wider optical classification for BL Lac than the one used for the 1 Jy and EMSS samples. This was a direct consequence of previous work on the ‘recognition problem’ which essentially affects flux limited samples by missing weak nuclear sources that lie buried in the core of bright galaxies (see Refs. 7 and 8 for a detailed description). Even though the relaxation of the optical criteria used in BL Lac selection has prevented some weak BL Lacs being missed in flux limited samples, it is clear we are far from understanding which are the physically meaningful parameters that hold the key to the BL Lac phenomenon. Very recently Ref. 9 have proposed a new optical classification scheme for BL Lacs which is based on the relation between the strength of [OIII] and [OII] emission lines which, the authors claim, is more closely related to the relevant physics of the sources. Even though this work constitutes a step forward in the search for physically meaningful selection criteria, the scheme deals only with the optical classification and it is therefore unlikely to sort out the biases introduced by the radio or X-ray selection of BL Lac samples. These are particularly important since the initial sample selection usually starts from either radio or X-ray (or both) surveys. The Spectral Energy Distribution (SED) of BL Lacs has long been modelled by two broad components: one extending from the radio frequency to the IR or even the X-rays and which is attributed to synchrotron emission, and another extending to the y-rays, and which is associated with Inverse
349 Compton processes. The analysis of the broad band properties and SEDs of BL Lacs has yielded that some sources have low frequency synchrotron peaks (LBL), whereas others have their synchrotron emission peaking at higher frequencies (HBL). Understanding why there is such a wide range of frequencies where the synchrotron emission can peak is probably one of the most puzzling issues in the study of the BL Lac population. However, before we understand the physics we need to understand the selection effects playing a role in the samples we are using to investigate the phenomenon. A good example may be the recently proposed spectral sequence for BL Lacs and flat radio spectrum quasars (usually grouped together and named ‘blazars’) involving the synchrotron peak frequency and luminosity. In fact, based on the few samples available at the time, Ref. 10 claimed that there was an anti-correlation between the peak frequency and the luminosity. This result even has an appealing theoretical explanation in terms of more luminous sources providing more inverse Compton cooling for the synchrotron electrons. However, could it be that the anti-correlation claimed by Ref. 10 be the consequence of selection effects ? The question is a pertinent one especially in view of the fact that the proposed sequence rests on the lack of a well sampled ‘peak frequency-luminosity’ plane. In other words, the samples available at the time of the analysis did not cover regions of the plane where sources with high luminosity and high peak frequencies, or with low luminosity and low peak frequencies, could be detected. One of the possible selection effects is actually well known in radio astronomy, i.e., high frequency surveys select primarily flat spectrum sources. On the other hand at the time Ref. 10 carried out the analysis, most of the HBLs were X-ray selected, and therefore less luminous sources, while most of the LBLs available were primarily from radio selected samples, hence more luminous sources. The combination of both of these facts could actually be working as a ‘conspiracy’ for creating a sequence involving the spectral properties and the luminosity. There are actually some indications that selection effects are indeed at the origin of the proposed sequence. Ref. 11 have found blazars with high luminosity, high peak frequency, and Ref. 12 have found sources that seem to be breaking the sequence at the low luminosity end.
3. S o , what have we learnt?
New and deeper samples of BL Lacs have been selected throughout the last few years. This effort has proven important because it provided us with a
350 view of a larger and wider range of the phenomenon than the one offered by the two initially available BL Lac samples. In the process we learnt that even if radio and X-ray surveys can select this class of AGN quite successfully, the required optical identification introduces biases that affect the statistical properties of the population. Although we have tried to relax the classification criteria in order not to miss weak BL Lac nuclei in the core of bright galaxies, we are still a long way from establishing what are the fundamental parameters that hold the key to the phenomenon. Also, during the last decade, possibly the most interesting feature of this type of sources has emerged: The synchrotron emission of BL Lacs (and flat radio spectrum quasars) can peak over a wide range of frequencies. The claim that there is an anti-correlation between the synchrotron peak frequency and the luminosity of the source backed by a physically appealing justification does not seem like it will stand the scrutiny of a better sampling of the ‘luminosity-peak frequency’ plane. Hence, it appears that despite the significant steps made towards a better knowledge of BL Lacs in particular, and of blazars in a more general way, we have to conclude that we are still dominated by selection effects and a larger effort is required to understand them before we are to understand the physics that govern the blazar phenomenon. References 1. M. Stickel, J.W. Fried, H. Kuehr, P. Padovani & C.M. Urry, ApJ 374,501 (1991). 2. S.L. Morris, J.T. Stocke, I.M. Gioia, R.E. Schild, A. Wolter, T. Maccacaro & R. della Ceca, ApJ 380,380 (1991). 3. S.A. Laurent-Muehleisen, R.I. Kollgaard, E.D. Feigelson, W. Brinkmann & J. Siebert, ApJ 525,127, (1999). 4. E.S. Perlman, P. Padovani, P. Giommi, RSambruna, L.R. Jones, A. Tzioumis & J. Reynolds, A J 115,125 (1999). 5. A. Caccianiga, T. Maccacaro, A. Wolter, R. della Ceca & I.M. Gioia, ApJ 513,51 (1999). 6. M.J.M. Marchl, A. Caccianiga, I.W.A. Browne & N. Jackson, MNRAS 326, 1455 (2001). 7. I.W.A. Browne & M.J.M.Marchl MNRAS 261,795 (1993). 8. M.J.M. Marchl & I.W.A. Browne MNRAS 275,951, (1995). 9. H. Landt, P. Padovani, E.S. Perlman & P. Giommi, MNRAS, in press. 10. G. Fossati, L. Maraschi, A. Celotti, A. Comastri & G. Ghisellini, MNRAS 299,433 (1998). 11. P. Padovani, E.S. Perlman, H. Landt, P. Giommi & M. Perri, ApJ 588,128 (2003). 12. A . Caccianiga & M.J.M. Marchl, MNRAS 348,937 (2004).
INTERMITTENCY, ACCRETION DISKS AND AGN EVOLUTION *
A. SIEMIGINOWSKA Center f o r Astrophysics., Cambridge, M A , 02138, USA E-mail:
[email protected]. edu A. JANIUK, B. CZERNY, M. SOBOLEWSKA AND R. SZCZERBA Copernicus Astronomical Center, Warsaw, Poland
There is growing evidence that AGN activity could be intermittent. We propose a scenario in which the accretion onto a supermassive black hole (SMBH) is unstable. The ionization instability in the accretion disk causes repetitive outbursts of activity followed by quiescence when the accretion flow becomes inefficient and the innermost parts of the disk evaporate. We calculate the evolution of the disk and provide characteristic timescales for the AGN activity.
1. Observational Evidence for AGN Intermittent Activity
Evidence for intermittent activity is growing. The morphology of Giant Radio Galaxies (e.g. B1545-321, 3C288, 3C424') which have outer lobes related to a relic and inner lobes to a current active phase, indicate feeding of the lobes on timescales of 107-108yrs. Compact Symmetric Objects (CSO) are thought to be young (is~compelling O evidence for a strong connection between the formation of the black hole and its host galaxy (e.g. [6,10]). Recent deep X-ray surveys imply that much of the growth of black holes has occurred relatively recently in AGN 365
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of modest luminosity.21 In our work, we have used the Sloan Digital Sky Survey (SDSS) to examine the relationship between galaxies, supermassive black holes, and AGN in the present-day Universe. The results presented in this paper have been published in a series of papers.3~9~11~'2~13 2. Methodology
We have used the SDSS Data Release One (DRll) to define a sample of -23,000 narrow line (Type 2) AGN from a r-band magnitude-limited sample of -123,000 galaxies for which SDSS spectra were obtained. Our methodology is described in detail in Kauffmann et al.13(herefafter K03) and Heckman et al.g (hereafter H04). We have used a grid of synthetic galaxy spectra to fit and remove the stellar contribution to the SDSS spectra, using the resulting emission-line spectrum to classify AGN (e.g. [2]). We use the luminosity a of the [OIII]X5007emission-line to measure AGN luminosity. Using the strong correlation in Type 1 AGN between Lo3 and Lopt in the SDSS23, and the bolometric correction to Lopt in [16], we derive a mean value L b o l / L ~ 3= 3500 in Type 1 AGN. We use the same correction factor for the Type 2 AGN in our ample.^^^^^^^ We use the stellar velocity dispersion measured within the central (typ3 t o 10 kpc) region to estimate the black hole mass, using the ically M B H - n relation of [20]. We only derive black hole masses for bulgedominated galaxies (see H04). With the black hole mass and bolometric luminosity, we can estimate the AGN luminosity in Eddington units. Assuming a radiative accretion efficiency of 10% (e.g. [22]), we can also estimate the accretion rate for each AGN. As diagnostics of the stellar population in the galaxies we have used two age-sensitive spectral features: 0,(4000) (the amplitude of the 4000A break) and H ~ (the A strength of the H6 absorption-line). The former index decreases monotonically as the luminosity-weighted mean age decreases, while the latter reaches a peak strength for a stellar population with an age of a few hundred Myr. These age-sensitive indices have been combined with the near-infrared (SDSS z-band) luminosity and the Bruzual &
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use Ho = 70 km s-l Mpc-l, f 2 = ~ 0.3, and $ 2 = ~ 0.7 throughout this paper. bWe will use the notation Lo3 when we correct only for foreground Galactic extinction and LO^,^,,^^ when we also correct for intrinsic extinction using the Balmer decrement (see K03).
367 Charlot4 models t o yield stellar masses ( M , ) and surface mass densities ( p * ) . See [Illfor details. In [3] we derived star formation rates for normal galaxies (non-AGN) from the Balmer emission-lines, and then showed that D, (4000) provided an excellent estimate of the specific star-formation rate ( S F R I M * ) . We use this relation to measure star-formation rates in the AGN hosts. We use the SDSS concentration index C as a rough proxy for Hubble type, with C > 2.6 and C < 2.6 corresponding to early-type galaxies (-E,SO and Sa) and late-type systems ( 4 b - I r r ) r e s p e ~ t i v e l y . ~ ~
3. Stellar Content of AGN Hosts As shown by [12], the SDSS galaxy population as-a-whole is strikingly bimodal. Galaxies with M* < 3 x 10’OMa (“low mass”) have low concentrations, low surface mass densities, and young stellar populations. Galaxies with M , > 3 x l0loMa (“high mass”) have high concentrations, high surface mass densities, and old stellar populations. Where do AGN hosts live in this landscape? As discussed in H04 and KO3 respectively, our sample of AGN is complete for Lo3 > 106La and for > 107L0. We will refer to AGN above (below) these fiducial luminosities as strong (weak) AGN. We find strong AGN are commonplace (-10% incidence rate) in high mass galaxies but much rarer in low mass galaxies. Most high mass galaxies are early types, and in KO3 we showed that AGN hosts have structural properties that strongly resemble those of normal early type galaxies of the same mass. However, while the host galaxies of weak AGN have the old stellar populations typical of high mass early type galaxies, KO3 showed that the hosts of strong AGN have a young stellar population signified by both a small 4000 A break and strong high-order Balmer absorption-lines. While a decreasing 4000 break amplitude with increasing AGN luminosity might be taken as evidence for dilution of the galaxy starlight by featureless AGN continuum, this it completely inconsistent with the increasingly strong Balmer absorption lines (which conclusively show the presence of a substantial population of young or intermediate age stars in strong AGN). Thus, strong AGN are preferentially hosted by galaxies that defy the general rule: they are massive galaxies with young stellar populations. Where is this young stellar population located in the host galaxies of strong AGN? KO3 selected two samples of strong AGN matched in and in M*. One sample was chosen to be nearby, with a typical z 0.03 to 0.04 (projected SDSS fiber diameter -2 kpc), while the other was much N
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more distant ( z 0.1 to 0.2, with a projected fiber diameter of 6 to 12 kpc). While only about half of the hosts had a young stellar population in the central kpc-scale region, nearly all of the hosts were young on larger scales. Thus, the star formation associated with AGN activity is not primarily confined t o the nuclear regions. As discussed in [ 111,the combination of our two age-sensitive diagnostics can be used t o identify galaxies that have undergone bursts of star formation within the last NGyr. Such systems are significantly displaced from the tight relation between 0,(4000) and H ~ defined A by normal galaxies. In KO3 we found that the fraction of such systems among the hosts of strong AGN was three times higher than among normal galaxies with the same stellar masses. In the standard AGN unified scenario, we would expect to see the same youthful stellar population in the hosts of comparably-powerful Type 2 and Type 1 AGN. Of course, it will be relatively difficult to study the stellar population in the hosts of powerful Type 1 AGN due to the blinding glare of the AGN itself. To explore this, KO3 constructed very high signal-to-noise composite spectra for samples of Type 1 and Type 2 AGN matched in Lo3 and redshift. We showed that the stellar populations of the two samples (in the mean) were indistinguishable.
4. Building Black Holes & Bulges
The results above are tantalizing in that they show that AGN activity and star formation are closely linked in galaxies. In this section we attempt to take our analysis one step further and study the relation between star formation and accretion onto black holes in a more quantitative way using our estimates for black hole mass, AGN bolometric luminosity, galaxy mass, and star formation rates described above. See H04 for details. We emphasize in what follows that we have only included Type 2 AGN in our census, and so will underestimate the total black hole growth rate by about a factor of two([7]; Hao et al., in preparation). Because powerful AGN are rare and the timescale over which black holes accrete most of their mass is likely to be considerably shorter than the timescale over which the surrounding galaxy forms its stars, it is more meaningful t o work with quantities that have been averaged over the volume sampled by the SDSS, rather than presenting results for individual AGN. That is, we are dealing quantities like the total accretion rate onto black holes per unit volume and the total mass in black holes per unit volume.
369 log (u/200 km/a) -0.4
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In Fig. 1, we plot the ratio of the volume-averaged LO3 luminosity in Type 2 AGN to the volume-averaged black hole mass in all galaxies as a function of log M B H . If we convert Lo3 into a mass accretion rate using the relations described above, we find that the present-day population of low mass black holes (< few x 107M,) have a growth (mass-doubling) time of only 30 Gyr, (2-3 times the age of the Universe). For more massive black holes (> 108M,), the growth timescales quickly increase to orders of magnitude larger than the Hubble time. This indicates that the most massive black holes must have formed at significantly higher redshifts and are currently experiencing very little additional growth. The population of low mass black holes is growing rapidly. If the very tight relation between black hole mass and bulge mass is t o be understood, it follows that low mass bulges hosting these black holes must also be rapidly growing. In Fig. 2, we plot the ratio of the volume-averaged star formation rate in all galaxies to the volume-averaged accretion rate onto black holes traced by Lo3 in Type 2 AGN. We have chosen t o plot SFR/hkBH as a N
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Figure 2. The ratio of the volume-averaged star formation rate in galaxies to the volume averaged accretion rate onto black holes in Type 2 AGN is plotted as a function of log M B H and log p * . The thick black line shows the result if SFR is calculated within the SDSS fiber aperture for each galaxy and the thin black lines shows the result using estimates of total SFR. The dashed lines show results restricted to the AGN with log Lo3 > 106.5Lo (where the bolometric correction is well-determined).
function of black hole mass M B H and surface mass density p,. From Fig. 2 it is clear that black hole growth is closely linked to star formation in the bulge. At low values of p, characteristic of disk-dominated galaxies 12, the ratio of SFR/ll;iBH rises steeply. This is because very few of these galaxies host AGN, but there is plenty of star formation taking , SFR/&fBH place in galaxy disks. At values of p* above 3 x 108M, kpc lo3, which is remains roughly constant. Moreover, it has a value of in good agreement with the empirically-derived relation between black hole mass and bulge mass15. Given the uncertainties in the bolometric correction and in the conversion from Lbol to black hole accretion rate, we find it remarkable that SFR/MBH comes out within a factor of a few of the value that is expected from the MBH-Mbulge relation!
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5 . Summary
Our results lead to a picture in which star formation and black hole growth in galaxies are strongly coupled. Strong AGN require two ingredients: a supermassive black hole and an abundant fuel supply in the form of cold interstellar gas. Thus, strong AGN are hosted by galaxies that are massive enough to have the former, but (unlike typical massive galaxies today) have a young stellar population made possible by the latter. We also find that both star formation and black hole growth have been moving to lower and lower galactic mass scales as we move forward in time from z -2 to the present. The most massive black holes are starving today
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and live in “dead” galaxies (giant ellipticals). In particular, our results show that the cosmic downsizing in the AGN population seen in recent deep Xray surveys21 is due to a decline with cosmic time in the characteristic mass scale at which black hole growth occurs (rather than just a drop in the characteristic Eddington ratio for the AGN population).
Acknowledgments Funding for the creation and distribution of the SDSS Archive has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Aeronautics and Space Administration, the National Science Foundation, the U.S. Department of Energy, the Japanese Monbukagakusho, and the Max Planck Society. The SDSS is managed by the Astrophysical Research Consortium (ARC) for the Participating Institutions. The Participating Institutions are The University of Chicago, Fermilab, the Institute for Advanced Study, the Japan Participation Group, The Johns Hopkins University, Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, University of Pittsburgh, Princeton University, the United States Naval Observatory, and the University of Washington.
References 1. K. Abazaijan et al., AJ 126, 2081 (2003). 2. J. Baldwin, M. Phillips & R. Terlevich, PASP 9 3 , 5 (1981). 3. J. Brinchmann e t al., MNRAS in press (2004). 4. G. Bruzual & S. Charlot, MNRAS 344, 1000 (2003). 5. R. Genzel et al., MNRAS317, 348 (2000). 6. G. Granato et al., MNRAS 324, 757 (2001). 7. L. H m , P h D Thesis, Princeton University (2003). 8. T. Heckman, ApJ446, 101 (1995). 9. T. Heckman et al., A p J s u b m i t t e d (2004). 10. G. Kauffmann & M. Haehnelt, MNRAS 311, 576 (2000). 11. G . Kauffmann et al., MNRAS 341, 33 (2003a). 12. G. Kauffmann et al., MNRAS 341, 54 (2003b). 13. G. Kauffmann et al., MNRAS 346, 1055 (2003~). 14. W. Keel, M. De Grijp, G. Miley & W. Zheng, A&A 283, 791 (1994). 15. A. Marconi & L. Hunt, ApJ 589, L21 (2003). 16. A. Marconi e t al., MNRAS in press (2004). 17. M. Miyoshi et al., Nature 373, 127 (1995). 18. J. Mulchaey e t al., ApJ436, 586 (1994). 19. I. Strateva e t al., AJ 122, 1861 (2001). 20. S. Tremaine et al., ApJ 574, 740 (2002). 21. Y. Ueda, A. Masayuki, K. O h t a & T . Miyaji, ApJ 598, 886 (2003). 22. Q. Yu & S. Tremaine, ApJ 335, 965 (2002). 23. N. Zakamska et al., AJ 126, 2125 (2003).
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Nancy Levenson
QUASAR HOST GALAXIES: RECENT RESULTS FROM HST
M. J. KUKULA Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ, UK E-mail:
[email protected] Since the discovery that most nearby massive spheroids harbour a black hole of proportionate mass, it has become clear that the co-evolution of galaxy spheroids and their central black holes is a key area in observational cosmology. Quasars offer a unique window on this evolution as they are the only class of object in which both galaxy and black-hole properties can be reliably measured out to high redshifts. For several years we have been conducting a programme of HST observations in order to determine the properties of quasar host galaxies across a large range of redshifts and quasar luminosities. Our sample now contains 60 quasars, including both radio-loud and radio-quiet objects, and spans redshifts from z=O.1 out to z=2 and absolute magnitudes from Mv -23 to -28. Here we summarise some of the recent results from this programme.
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1. Low-redshift quasar hosts The study of quasar host galaxies requires the accurate separation of light from the bright active nucleus from the surrounding halo of starlight. Thus good angular resolution and a stable, well-defined point spread function (PSF) are clearly desirable, and for this reason it is largely due to the efforts of the Hubble Space Telescope (HST) that the host galaxies of quasars in the local universe are now so well understood. Comprehensive studies of low redshift ( z < 0.3) quasar hosts have now been carried out (e.g. Disney et al. 1995; Hutchings & Morris 1995; Bahcall et al. 1997; Hooper et al. 1997; McLeod et al. 1999; Hamilton et al. 2002) and all indicate that powerful nuclear activity in nearby galaxies is usually associated with massive, bulgedominated hosts. This ties in well with the recent confirmation in inactive galaxies of a correlation between the mass of the galaxy spheroid and that of its central black hole (e.g. Kormendy & Gebhardt 2001). The host galaxies uncovered by HST are exactly the type of systems in which one would
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374 expect to find the very massive black holes required to power luminous quasars. Our own HST programme, carried out in Cycle 6, was designed to determine the host galaxy properties of 23 moderately luminous low-redshift (z 0.2) quasars (McLure et a\. 1999; Dunlop et al. 2003). This study has provided the most compelling evidence to date that quasar activity in the local universe is associated with massive spheroidal galaxies. We found that the hosts of all quasars more luminous than M R = -24 are massive elliptical galaxies with L > L*, irrespective of the radio power of the quasar (McLure et al. 1999; Dunlop et al. 2003). The colours & spectra of the hosts are also identical to those of local inactive ellipticals (e.g. Nolan et al. 2001). It seems that low-redshift quasars are simply a rare, currently active subset of the local elliptical galaxy population. In this paper we summarize our recent efforts to extend this work to higher quasar luminosities and higher redshifts, with new HST programmes in Cycles 7, 9 & 10. Figure 1 shows how these studies are allowing us to explore the luminosity/redshift plane for quasars and to examine independently the effects of nuclear luminosity and cosmological evolution upon their host galaxies. N
2. Quasar host galaxies as probes of galaxy evolution Far from being a sideline of galaxy research, quasar hosts provide an invaluable tool for studying the history of massive galaxies over large intervals of cosmological time, and particularly for investigating the way in which the black-hole/spheroid mass relation has evolved from early epochs down to the present day. This is because quasars are the only high-redshift objects for which we can obtain reliable estimates of both galaxy mass (via the luminosity and colours of their hosts) and black-hole mass (from the emission line widths of broad-line clouds in the inner few parsecs). To date, most studies of the black-hole/spheroid mass ratio have focussed on inactive galaxies in the local universe, where the relationship is easiest to measure. Theoretical models of black-hole/spheroid formation and growth can be tuned to reproduce the mass relation observed at z = 0 (e.g. Kauffmann & Haehnelt 2000; Archibald et al. 2002; Granato et al. 2004) but the empirical information required to verify or refute such models can only come from observational determination of the mass relation at higher redshifts, where it is believed that the bulk of galaxy and star formation occurs. Active galaxies - in the form of quasars - therefore provide
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Figure 1. Absolute magnitude versus redshift for the quasars observed to date in our HST host galaxy programs. The various symbols denote different quasar subsamples, all of which were observed with an instrument/filter combination which targetted V-band in the object's rest frame. Open circles show the low-redshift, moderat+luminosity quasars from our original Cycle 6 study; triangles indicate the quasar subsamples at redshifts of 1 & 2 observed with NICMOS and WFPCZ in Cycles 7 and 10; stars show the Cycle 9 quasar subsample at z 0.4,the lowest redshift at which representatives of the most luminous quasars can be found. Note how the various subsamples probe two orthogonal directions in this parameter space, allowing us t o explore the effects on host galaxy properties of both redshift and quasar luminosity. N
a unique opportunity to explore how the black-hole/spheroid mass relation actually evolves, and this was the goal of our Cycle 7 HST programme, carried out with the Near Infrared Camera and Multi-Object Spectrograph (NICMOS).
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3. Observing quasar hosts out t o z -2 with NICMOS We began by defining two new samples of quasars a t redshifts of 1 & 2, all with absolute V-band magnitudes in the range -24 > MV > -25, making them comparable in optical power to the majority of the quasars in our previous low-redshift sample at z 0.2 (Figure 1). By observing in the near-IR we were able to target the object's restframe V-band, and thus to detect the mass-dominant stellar population of the hosts at rest wavelengths longwards of 4000A (Kukula et al. 2001). N
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Figure 2. Mean absolute magnitude versus redshift for the quasar host galaxies at redshifts of 0.2 (Cycle 6) and 1 & 2 (Cycle 7). The dotted lines show passive evolutionary curves for present-day L*, 2L* and 4L* ellipticals, assuming they formed in a single starburst event at z 5.
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Earlier predictions based on semi-analytic models of hierarchical merging suggested that the hosts of quasars at z = 2 would be several times smaller and less massive than their counterparts at low z . In fact we find that both radio-loud and radio-quiet quasars at z = 2 are already surrounded by large, luminous galaxies (Figure 2) - a result which also emerges from the studies of Ftidgway et al. (2001) and Falomo et al. (2003). To translate these galaxy luminosities into masses requires that we first determine the stellar composition of the hosts. In Cycle 10 we reobserved our quasar sample with HST/WFPC2 in order to provide galaxy colours straddling the spectral break at (restframe) 4000A - a feature which is very sensitive to the age of the stellar population. Results from this study
377 suggest that, even at redshifts of 4,the hosts are also already quite passive, red systems (Kukula et al. 2004, in preparation). Overall, it seems that much of the star formation in these massive host galaxies must have occurred at redshifts >2. This is consistent with recent studies of radio galaxies (de Vries et al. 2000; Zirm et al. 2003) as well as deep groundbased surveys of inactive galaxies which find highly evolved systems at similarly high redshifts (eg. Glazebrook et al. 2004). We are currently conducting a programme of nuclear spectroscopy with the same quasars to obtain virial mass estimates for the central black holes from the width of their broad MgII lines.
4. The hosts of luminous quasars
The star symbols in Figure 1 represent our most recent HST study of quasar hosts - a deep WFPC2 imaging study of 17 quasars at z 0.4, carried out in Cycle 9 (Floyd et al. 2004). The sample consists of quasars with absolute magnitudes in the range -24 2 MV 2 -28, allowing us to investigate host galaxy properties across a decade in quasar luminosity, but at a single redshift. As Figure 1 shows, our previous imaging studies of AGN hosts largely focussed on moderate luminosity quasars, where the separation of nuclear and host galaxy components is relatively straightforward. By contrast the most powerful objects in the Cycle 9 sample are comparable to the most luminous quasars found at very high redshifts. Despite the additional difficulties involved in analysing the images of these very luminous objects we have been able to obtain robust measurements of the sizes, morphologies and luminosities of their host galaxies. Once again we find that the host galaxies of all radio-loud quasars, and all radio-quiet quasars more luminous than MV = -25, are massive ellipticals with luminosities > L*. Unsurprisingly, the increase in quasar luminosity by a factor of 10 across the sample is not entirely due to a corresponding increase in host galaxy and thus black hole mass (such massive galaxies would be exceedingly rare in any case). Instead the most luminous quasars in our sample also seem to be radiating roughly three times as efficiently as their less powerful counterparts. This is the first time that the host galaxy properties of such powerful quasars have been successfully recovered, and represents an important step towards future studies of quasar hosts at very high redshifts (> 2), where the majority of known quasars are necessarily extremely luminous. N
378 5 . Summary
To date, we have imaged 60 quasars with HST, allowing us t o determine the properties of their host galaxies from redshifts of 0.2 out to 2, and across a decade in quasar luminosity. T h e study has confirmed t h a t powerful nuclear activity is confined t o massive, bulge-dominated galaxies, t he majority of which appear t o have formed at high redshifts.
References 1. E.N. Archibald, J.S. Dunlop, R. Jimenez, A.C.S. Friaca, R.J. McLure & D.H. Hughes, MNRAS 336, 353 (2002). 2. J.N. Bahcall, S. Kirhakos, D.H. Saxe & D.P. Schneider, ApJ479, 672 (1997). 3. M.J. Disney, P.J. Boyce, J.C. Blades, A. Boksenberg, P. Cane, J.M. Deharveng, F. Macchetto, C.D. Mackay, W.B. Sparks & S. Phillipps, Nature 376, 150 (1995). 4. J.S. Dunlop, R.J. McLure, M.J. Kukula, S.A. Baum, C.P. O'Dea & D.H. Hughes, MNRAS 340, 1095 (2003). 5. R. Falomo, N. Carangelo & A. Treves, MNRAS 343, 505 (2003). 6. D.J.E. Floyd et al., MNRAS submitted (2004). (astro-ph/0308436) 7. K. Glazebrook et al., (astro-ph/0401037) (2004). 8. G.L. Granato, G. De Zotti, L. Silva, A. Bressan & L. Danese, ApJ 600, 580 (2004). 9. T.S. Hamilton, S. Casertano & D.A. Turnshek, A p J 576, 61 (2002). 10. E.J. Hooper, C.D. Impey & C.B. Foltz, A p J 480, L95 (1997). 11. J.B. Hutchings & S.C. Morris, A J 109, 1549 (1995). 12. G. Kauffmann & M. Haehnelt, MNRAS 311, 576 (2000). 13. J. Kormendy & K. Gebhardt, AIP Conf. Proc. 586, 363 (2001). 14. M.J. Kukula, J.S Dunlop, R. J. McLure, L. Miller, W.J. Percival, S.A. Baum & C.P. O'Dea, MNRAS326, 1533 (2001). 15. K.K. McLeod, G.H. Rieke & L.J. Storrie-Lombardi, A p J 511, L67 (1999). 16. R.J. McLure, M.J. Kukula, J.S. Dunlop, S.A. Baum, C.P. O'Dea & D.H. Hughes, MNRAS 308, 377 (1999). 17. L.A. Nolan, J.S. Dunlop, M.J. Kukula, D.H. Hughes, T. Boroson & R. Jimenez, MNRAS 323, 308 (2001). 18. S. Ridgway, T. Heckman, D. Calzetti & M. Lehnert, A p J 550, 122 (2001). 19. W.H. de Vries, C.P. O'Dea, P.D. Barthel, C. Fanti, R. Fanti & M.D. Lehnert, A J 120, 2300 (2000). 20. A. Zirm, M. Dickinson & A. Dey, A p J 585, 90 (2003).
A PHYSICAL MODEL FOR THE JOINT EVOLUTION OF QSOS AND SPHEROIDS
G.L. GRANATO INAF-Padova, Vicolo osservatorio 5, I-35122 Padova, Italy
L. SILVA INAF- Pieste, Via Taepolo 11, 1-34131 Pieste, Italy
L. DANESE SISSA, Via Beirut
4,
I-34014 Pieste, Italy
G. DE ZOTTI INAF-Padova, Vacolo Osservatorio 5, 1-35122 Padova, Italy A. BRESSAN INAF-Padova, Vicolo Osservatorio 5, 1-35122 Padova, Italy We summarize our physical model for the early cc-evolution of spheroidal galaxies and of active nuclei at their centers. Our predictions are in excellent agreement with a number of observables which proved to be extremely challenging for all the current semi-analytic models, including the sub-mm counts and the corresponding redshift distributions, and the epoch-dependent K-band luminosity function of spheroidal galaxies. Also, the black hole mass function and the relationship between the black hole mass and the velocity dispersion in the galaxy are nicely reproduced. The mild AGN activity revealed by X-ray observations of SCUBA sources is in keeping with our scenario, and testify the build up of SMBH triggered by intense star formation.
1. Introduction
The standard Lambda Cold Dark Matter (ACDM) cosmology is a well established framework to understand the hierarchical assembly of dark matter (DM) halos. Indeed, it has been remarkably successful in matching the observed large-scale structure. However, the complex evolution of the baryonic matter within the potential wells determined by DM halos is still 379
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an open issue, both on theoretical and on observational grounds. Full simulations of galaxy formation in a cosmological setting are far beyond present day computational possibilities. Thus, it is necessary to introduce at some level rough parametric prescriptions to deal with the physics of baryons, based on sometimes debatable assumptions. A class of such models, known as semi-analytic models, has been extensively compared with the available information on galaxy populations at various redshifts (see Granato et al. 2000 and references therein). The general strategy consists in using a subset of observations to calibrate the many model parameters providing a heuristic description of baryonic processes we do not properly understand. Besides encouraging successes, current semi-analytic models have met critical inconsistencies which seems to be deeply linked to the standard recipes and assumptions. These problems are in general related to the properties of elliptical galaxies, such as the color-magnitude and the [a/Fe]-M relations (Cole et al. 2000; Thomas 1999), and the statistics of sub-mm and deep IR selected (I- and K-band samples). These data would be more consistent with the traditional “monolithic” scenario, according to which elliptical galaxies formed most of their stars in a single burst, at relatively high redshifts, and underwent essentially passive evolution thereafter. However the strict “monolithic” scheme cannot be fitted in a consistent model for structure formation from primordial density perturbations. However, the general agreement of a broad variety of observational data with the hierarchical scenario and the fact that the observed number of luminous high-redshift galaxies, while substantially higher than predicted by semi-analytic models, is nevertheless consistent with the number of sufficiently massive dark matter halos, indicates that we may not need alternative scenarios, but just some new ingredients. Previous work by our group (Granato et al. 2001; Romano et al. 2002; Granato et al. 2004) suggests that a crucial ingredient is the mutual feedback between spheroidal galaxies and active nuclei at their centers. important clues to understand the formation and evolution of spheroids arise from the now well established correlation between their stellar mass (or velocity dispersion) and the mass of the supermassive black hole (SMBH) hosted in their centers, and responsible for high-z quasar activity. Granato et al. (2004, henceforth GDS04) presented a detailed physically motivated model for the early co-evolution of the two components, in the framework of the ACDM cosmology. The model has been built follow-
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Figure 1. Scheme of the baryonic components included in the model (boxes), and of the corresponding mass transfer processes (arrows). The numbers near the arrows point to the main equations describing those processes in Granato et al. (2004).
ing suggestions of a scenario previously explored with a partly empirical approach (Granato et al. 2001).
2. Model description
The model follows with simple, physically grounded, recipes and a semianalytic technique the evolution of the baryonic component of protospheroidal galaxies within massive dark matter (DM) halos forming at the rate predicted by the standard hierarchical clustering scenario for a ACDM cosmology. The main difference with respect to other models is the central role attributed to the mutual feedback between star formation and growth of a super massive black hole (SMBH) in the galaxy center. Indeed, the treatment include plausible prescriptions for the chain of processes leading to SMBH growth trough accretion, and for the effects on the ISM of the ensuing QSO activity. A scheme of the baryonic components included in the model, and of the relevant transfer processes is shown in Fig. 1. The kinetic energy fed by supernovae is increasingly effective, with decreasing halo mass, in slowing down (and eventually halting) both the star formation and the gas accretion onto the central black hole. On the contrary, star formation and black hole growth proceed very effectively in the more massive halos, until the energy injected by the active nucleus in the surrounding interstellar gas unbinds it, thus halting both the star formation and the black hole growth (and establishing the observed relationship between black hole mass and stellar velocity dispersion or halo mass, see
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Figure 2. Left: predicted relationship between black-hole mass and line-of-sight velocity dispersion of the host galaxy for different virialization redshifts. Right: Predicted redshift distribution of galaxies brighter than K = 20 compared with the results of the K20 survey
Fig. 2). As a result, the physical processes acting on baryons reverse the order of the formation of spheroidal galaxies with respect to the hierarchical assembling of DM halos, in keeping with the previous proposition by Granato et al. (2001). Not only the black hole growth is faster in more massive halos, but also the feedback of the active nucleus on the interstellar medium is stronger, to the effect of sweeping out such medium earlier, thus causing a shorter duration of the active star-formation phase (for more details, see GDS04). According to GDS04 (as well as Granato et al. 2001), the high redshift QSO activity marks and concur to the end of the major episode of star formation in spheroids. Thus there is a clear evolutionary link between the SCUBA sources and high-z QSOs. Indeed, the proposed scenario is based on a close and circular relationship between star formation activity, BH growth and feedback of the AGN activity on star formation. This relationship manifest itself as a a well defined and distinctive sequence connecting various populations of massive galaxies: (i) virialization of DM halo; (ii) vigorous and rapidly dust-enshrouded star formation activity, during which a central SMBH grows; (iii) QSO phase halting subsequent star formation and (iv) essentially passive evolution of stellar populations, passing through an Extremely Red Object (ERO) phase. As demonstrated by GDS04, this scenario fits nicely two very important populations at high redshift, which are extremely problematic for standard semi-analytic models (e.g.
383 Somerville, 2004): vigorously star- forming, dust-enshrouded starbursts (in practise SCUBA sources; stage (ii)) and quiescent red spheroids (stage iv). Also, the epoch dependent luminosity function of spheroids and the local mass function of SMBHs is well reproduced. On the other hand, the general consistence of this sequence with high redshift QSO population has been investigated by Granato et al. (2001), while a detailed analysis is the subject of papers in preparation. In the next section, we analyze as an example the SMBH growth during stage (ii), as traced by X-ray observations of sub-mm selected sources.
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Figure 3. Number counts predicted by GDS04 model for SCUBA sources with amretion rates greater than several thresholds. Solip: all sources; dash: M > 0.02Moyr-'; dot>I 0.2Mayr-l; three dot-dash: M > 1Mayr-' > 1046ergs-l). See text dash: & for explanations.
3. AGN sctivity in SCUBA sources The model predicts the overall time development of AGN activity in forming spheroids, though precise predictions in most electromagnetic bands are made uncertain by environmental effects, that can significantly influence the way this activity shows up. This is particularly true in our scenario, since the QSO growth occurs in a rather extreme ambient, with no obvious analog in the local universe. The situation is relatively more favorable with X-ray photons, especially HX ones, which are the less affected by interactions with the ISM, and are less likely to be confused with those
384 produced by processes directly connected with SF, such as X-ray binaries. Recently Alexander et al. (2003) noticed that a fraction 30 - 50% of bright (> 5 mJy) SCUBA sources hosts mild AGN activity, with X ray (0.58 keV) intrinsic luminosity between erg s-'. Using a plausible and bolometric correction of &,ol/LX[0.5 - 8keV] N_ 20 (Marconi et al. 2004) and with the accretion efficiency 0.1-0.15 adopted by GDS04 (quite standard), these figures translate into accretion rates onto the central SMBH of 0.02-0.2 M a yr-'. Fig. 3 shows number counts for SCUBA sources with accretion rates greater than several thresholds, and demonstrates that our model is fully consistent with Alexander et al. findings. Indeed, almost all SCUBA sources brighter than 2~ 5 mJy are expected t o host an AGN with intrinsic Lx[O.5 - 8keVI > (dashed line in Fig. 3), leaving room for sources with high column density. According to our interpretation, the moderate AGN activity revealed by X-ray observations in many bright SCUBA sources corresponds t o the build up by accretion of the central SMBH, induced by star formation, and well before the bright QSO phase that cause the end of the major epoch of star formation in these objects.
Acknowledgments
G.L. Granato and L. Silva thank INAOE for financial support and kind hospitality. References 1. D.M. Alexander et al., AJ 125, 383 (2003). 2 . S. Cole, C.G. Lacey, C.M. Baugh & C.S. F'renk, MNRAS 319, 168 (2000). 3. G.L. Granato, C.G. Lacey, L. Silva, A. Bressan, C.M. Baugh, S. Cole & C.S. F'renk, ApJ 542, 710 (2000). 4. G.L. Granato, L. Silva, P. Monaco, P. Panuzzo, P. Salucci, G. De Zotti & L. Danese, MNRAS 324, 757 (2001). 5 . G.L. Granato, G. De Zotti, L. Silva, A. Bressan & L. Danese, ApJ 600, 580 (2004, GDS04). 6. A. Marconi et al., MNRAS351, 169 (2004). 7. D. Romano et al., MNRAS 334, 444 (2002). 8. L. Silva, G.L. Granato, A. Bressan & P. Panuzzo, RMxAC 17, 93 (2003). 9. R.S. Somerville, astro-ph/0401570 (2004). 10. D. Thomas, MNRAS 306, 655 (1999).
BLACK HOLE MASSES OF HIGH-REDSHIFT QUASARS
M. VESTERGAARD Steward Observatory
933 N . Cherry Avenue, Tucson, AZ, 85721, USA E-mail: mvestergaard@as. arizona. edu Black-hole masses of distant quasars cannot be measured directly, but can be estimated to within a factor 3 to 5 using scaling relationships involving the quasar luminosity and broad-line width. Why such relationships are reasonable is summarized. The results of applying scaling relationships to data of quasars at a range of redshifts ( z 5 6.3) are presented. Luminous quasars typically have masses 109M0 even at the highest redshifts. The fact that such massive black holes appear as early as at z x 6 indicate that black holes form very early or build up mass very fast.
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1. Introduction With our recently acquired ability to measure black-hole masses in nearby quiescent and active galaxies we are now in a position to start addressing the important issues of the physics of black-hole evolution and the possible role of black holes in how galaxies evolve. An important first step is to establish the typical mass of black holes in AGNs at high redshift relative to more nearby AGNs. Such a study1 is summarized here. 2. Mass Estimates The most robust method to determine the mass of the central black hole in active galaxies is that of reverberation mapping. However, this method is impractical for large samples of luminous and distant quasars as it takes many years to measure quasar masses. The reasons are that luminous quasars vary with smaller amplitudes and on longer time scales that are further increased by time dilation due to their cosmological distances. Mass estimates based on single-epoch data are therefore very useful, even if less accurate. Of the “secondary mass estimators’’ used in the literature only a couple are useful at high redshift, as reviewed by Vestergaard2. The “scaling 385
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relations’’ used here also appear the most promising at present given their relatively lower and readily quantifiable associated uncertainties’. Scaling relations are approximations to the virial mass ( M oc v’R) determination of the reverberation mapping method, where the light travel time delay, r = R/c, between continuum and line variations determine the distance R of the line-emitting gas and the line width of the variable part of the line profile, the RMS profile, yields the velocity dispersion v of the same varying gas. Instead, scaling relations use the empirical radius - luminosity relationship3, where R 0: and single-epoch measurements of the line width and the continuum luminosity to estimate the black-hole mass. Vestergaard4 calibrated single-epoch mass estimates based on H ,f3 and C IV line widths, respectively, to the more accurate reverberation masses. The associated statistical uncertainty is a factor 3 relative to the reverberation masses (i.e., a factor N 5 on an absolute scale). However, mass estimates of individual objects can be in error up to a factor of 10. The mass estimates presented below are based on these two relations. Contrary to the belief of some, scaling relations are reasonable, even those based on UV spectroscopy for the following reasons. First, contemporaneous UV-optical monitoring of NGC 5548, the best-studied nearby Seyfert, shows that all the broad lines measured (Si rvX1400, C IVX1549, He 11x1640, C III]X1909, H pX4861, He 11x4686) are consistent with virial motion of the broad-line r e g i ~ n ~higher ? ~ : ionization lines are emitted closer to the central source and have larger Doppler widths. Second, this virial relationship is seen for all (four) AGNs that can be t e ~ t e d ~and > ~ yso~it is fair to assume the relationship is universal, even if the sample is small. Third, since the virial product (w’T) is constant for each AGN, the velocity dispersions and the response-lag scale between the emission lines. Finally, the R- L relation extends also to high redshift and high luminosity quasars because (1)quasar spectra are very similars at all redshifts and luminosities considered here, and (2) the most luminous quasars have luminosities not much larger ( 5 1.5dex) than the luminosity range over which the R - L relationship is defined’ . See Veste~gaard~>’>~ for further details. N
3. Quasar Samples and Data In the following, mass estimates are presented for different samples of quasars spanning the redshift range 0 5 z 5 6.2: the Bright Quasar Survey (BQS) of 87 objects at z 5 0.5, a sample of 114 1.5 5 z 5 3.5 quasars almost equally distributed among radio-quiet and radio-loud sources, and
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Figure 1. Distributions of estimated (a) black-hole mass, (b) bolometric luminosity, and (c) Eddington ratio for different redshift bins ( H o = 75 km s-lMpc-', qo = 0.5, and A = 0). In the middle panel the radio-quiet subset is shown shaded to illustrate that the two radio types do not differ in these parameters as claimed earlier (e.g., [12]).
-150 z M 4 quasars from recently published samples which include objects and data from the Sloan Digital Sky Survey. See Vestergaard' for details. Bolometric luminosities were estimated using bolometric corrections to restframe UV luminosities, based on average spectral energy distributionslO, updated to include a more realistic X-ray energy distribution1'. 4. Masses of Distant Quasars
Figure 1 shows that the luminous quasars at z > 1.5 are similarly distributed in black-hole mass M B H ,bolometric luminosity and Eddington ratios (&,ol/LEdd) with an average mass of 1 0 9 ~ and @ luminosity of 1047ergss-1. While the lower limits in M B Hand Lbol are due to the sample selection and survey limits, the data show the important fact that the luminous, distant quasars that we can detect are equally massive as the lower redshift quasars, even beyond the epoch ( z 2 3) where the comoving quasar space density drops. Moreover, there are characteristic, but real, ceilings at MBH M loloMa and &,o] M 1O4*ergss-'. 5 . Mass Functions
Vestergaard, Osmer, and Fan (in preparation) are currently determining mass functions of active black holes at different redshifts. Our first results show that the BQS, Large Bright Quasar Survey (LBQS), and colorselected SDSS samples exhibit consistent mass functions (Fig. 2; HO = 50 km s-lMpc-', qo = 0.5, A = 0 ) . The goal is to constrain black-hole growth by combining theoretical models (see Steed this volume) with measurements from large data bases.
~
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0 lsQs (,=l.l-Z.O) 0 SDSS ( ~ 8 . 6 - 6 . 0 )
1
Figure 2. Mass functions of the BQS, LBQS (preliminary), and the color-selected SDSS sample ( I f 0 = 50 km s-lMpc-', qo = 0.5, A = 0). The low-mass turn-down for more distant LBQS quasars is an artifact owing to the lower flux-limit of the sample. 6. Conclusions
The two main conclusions from this work are: (1) Black-hole masses in nearby AGNs can be measured to within a factor 3. For more distant AGNs, useful mass estimates can be obtained to within a factor of 3 to 5. Even if less accurate, mass estimates are particularly useful for statistical studies. (2) Black holes of luminous quasars are very massive (N lO9M@)even at the highest redshifts of 4 to 6. The existence of such massive black holes at these early epochs indicate that they formed very early or very fast.
References 1. 2. 3. 4. 5. 6.
M. Vestergaard, ApJ 601, 676 (2004). M. Vestergaard, preprint (2004). (astro-ph/0401436) S. Kaspi et al., ApJ533, 631 (2000). M. Vestergaard, A p J 571, 733 (2002). B.M. Peterson & A. Wandel, ApJ 521, L95 (1999). B.M. Peterson & A. Wandel, A p J 540, L13 (2000). 7. C. Onken & B.M. Peterson, A p J 572, 746 (2002). 8. M. Dietrich et al., A p J 581,912 (2002). 9. M. Vestergaard, preprint (2004). (astro-ph/0401430) 10. M. Elvis et al., ApJS 95, 1 (1994). 11. M. Elvis, G. Risaliti & G. Zamorani, ApJ 565, L75 (2002). 12. A. Laor, ApJ543, L l l l (2000).
THE COSMOLOGICAL EVOLUTION OF QUASAR BLACK-HOLE MASSES
R. J. MCLURE AND J.S. DUNLOP Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh, EH9 3HJ, UK E-mail:
[email protected] Virial black-hole mass estimates are presented for 12698 quasars in the redshift interval 0.1 5 z 5 2.1, based on modelling of spectra from the Sloan Digital Sky Survey (SDSS) first data release. The black-hole masses of the SDSS quasars are found to lie between N lo7 M g and an upper limit of N 3 x lo9 M a , entirely consistent with the largest black-hole masses found to date in the local Universe. The estimated Eddington ratios of the broad-line quasars (FWHM _> 2000 km s-l) show a clear upper boundary at L b o l / L E d d N 1, suggesting that the Eddington luminosity is still a relevant physical limit to the accretion rate of luminous broad2. By combining the black-hole mass distribution of the line quasars at z SDSS quasars with the 2dF quasar luminosity function, the number density of active black holes at z N 2 is estimated as a function of mass. By comparing the estimated number density of active black holes at z N 2 with the local mass density of dormant black holes, we set lower limits on the quasar lifetimes and find that the majority of black holes with mass _> 10s.5 M g are in place by 21 2.
lo9 M a already in the first quasars.
Currently, the most distant quasars known are located at redshifts of almost 6.5 (Fan et al. 2003). Already at this early stage of the Universe’s evolution, in the center of these quasars super-massive black holes of > 109Ma are present (Fan et al. 2001; Brandt et al. 2002a;b; Willot et al. 2003). Physical model. Guided by the results of merger model calculations by Barnes & Hernquist (1996, 1998) and Barnes (2002), we make the assumption that, due to a major merger, tidal forces have driven a large amount Ma) of ISM into the central region (within a few hundred parsec of the center) of the newly formed merged galaxy. We follow the evolution of a self-gravitating accretion disk which results from the merger. It has been known for quite a while that a standard accretion disk (“a-disk”) evolves far to slowly to be of any relevance for an accretion driven growth of a central black hole (Shlosman et al. 1989, 1990). Instead, here we use the Reynolds number based viscosity prescription proposed by Duschl et al. (1998, 2000) and Richard & Zahn (1999). We allow also for advection dominated accretion (Beckert & Duschl 2002). Accretion disk evolution and black hole growth. We performed numerical model calculations and present a typical example in Fig. 1. The initial disk mass is 1O1OM@and the viscosity parameter ,B = For numerical convenience we assumed a seed black hole of lo3 Ma. The final *This work is supported by Deutsche Forschungsgemeinschaft (DFG) through the Sonderforschungsbereich “Galaxies in the Young Universe” (SFB 439)
393
394 black hole mass is determined mainly by the length of an initial Eddington limited accretion phase. We find that this type of accretion disk allows for a sufficiently fast growth of a super-massive black hole. The high-luminosity phase ends rather abruptly when radial advection of energy becomes important, limiting the high-luminosity phase t o some lo8 years. A much more detailed account of this work will be presented in Duschl & Strittmatter (2004, in prep.).
Time f Iyr]
Figure 1. Evolution of luminosity (full line) and black hole mass (broken line) as a function of time. For the disk parameters, see the text.
References 1. J.E. Barnes, MNRAS 333, 481 (2002). 2. J.E. Barnes & L. Hernquist, ApJ471, 115 (1996). 3. J.E. Barnes & L. Hernquist, A p J 4 9 5 , 187 (1998). 4. T. Beckert & W.J. Duschl, A&A 387, 422 (2002). 5. W.N. Brandt et al., A p J 569, L5 (2002a). 6. W.N. Brandt et al., MPE-Report 279,235 (2002b). 7. W.J. Duschl, P.A. Strittmatter & P.L. Biermann, BAAS 30, 917 (1998). 8. W.J. Duschl, P.A. Strittmatter & P.L. Biermann, AHA 357, 1123 (2000). 9. X. Fan et al., AJ 122,2833 (2001). 10. X. Fan et al., AJ 125, 1649 (2003). 11. D. Richard & J.-P. Zahn, A&A 347, 734 (1999). 12. I. Shlosman, M.C. Begelman & J. Frank, Nature 345, 679 (1990). 13. I. Shlosman, J. Frank & M.C. Begelman, Nature 338, 45 (1989). 14. C.J. Willot, R.J. McLure & M.J. Jarvis, ApJ 587, L15 (2003).
BVRI SURFACE PHOTOMETRY OF MIXED MORPHOLOGY PAIRS OF GALAXIES: INTERACTIONS, MERGERS AND NUCLEAR ACTIVITY
A. FRANCO-BALDERAS, D. DULTZIN-HACYAN AND H. M. HERNANDEZ-TOLEDO IA-UNAM, Apartado Postal 70-264, Mkxaco DF-04510, Mkxaco; alfred @astroscu.unam. m x In order to analyze the photometric signature of gravitational interactions in spiral and elliptical galaxies, we present results of multicolor broad band (BVRI) surface photometry for a set of 42 mixed pairs drawn from the Karachentsev Catalogue of Isolated Pairs of Galaxies (KPG, [3]). It is generally believed that a high percentage of AGN have close neighbors implying an AGN-interaction connection. The presence of these galaxies in mixed pairs (13 of 84 in our sample) supports the notion that the triggering mechanism for their nuclear activity is of tidal origin and that it does not depend strongly on the type of perturbing galaxy.
1. Introduction Mixed pairs are excellent laboratories for the study of interaction in galaxies because they represent a set of systems in which we see the effects of the interaction of a gas rich object (S member) in the presence of a relatively clean disturber (E/SO member). Measurements of surface brightness profiles are essential for quantitative investigations of galaxy morphology, decomposition of bulge and disk, galaxy structure and stellar populations, and dust distribution. Our observations will help t o determine important parameters like the size, the distribution of mass, the star formation rate, as well as the magnitude of nuclear activity. We propose to use algorithms to filter the B-band images, in combination with the estimated geometric and surface brightness profiles, t o look for morphological features in more detail [2]. 2. Interactions and mergers
Most mixed pairs show signs of disturbance like bridges, tails, geometric and morphologic distortions, and in some cases nuclear activity which give 395
396 us evidence of gravitational interactions. A significant number of galaxies in our sample (13 of 84) show nuclear activity as a result of interaction. In some cases, we have evidence of cross-fuelling [l].
Figure 1. Left: B-band image of KPG 552. Right: Numerical simulation of the interaction between two spirals.
3. Numerical Simulations and Nuclear Activity Numerical simulations support a cross-fuelling scenario for KPG 552 (Fig. 1). KPG 552A is a Seyfert 2 galaxy. The surface brightness profile of KPG 552B reveals its elliptical nature. Surprisingly, it is also a Seyfert 2 galaxy. The simulation shown in Fig. 1 represents the interaction between two spiral galaxies [4]. Apparently, the perturbation induced in the target galaxy does not depend strongly on the morphological type of the perturbing galaxy: an elliptical in the case of KPG 552B, and a spiral in the simulation.
References 1. D.L. Domingue et al., AJ 125, 555 (2003). 2. A. Franco-Balderas, D. Dultzin-Hacyan, H.M. Hernfindez-Toledo & G. GarciaRuiz, A&A 406, 415 (2003). 3. I.D. Karachentsev, Catalogue of Isolated Pairs of Galaxies in the Northern Hemisphere, Comm. Spec. Ap. Obs. 7,1 (1972). 4. T. Naab & A. Burkert, A p J 5 5 5 L , 91 (2001).
STUDY OF STELLAR POPULATIONS IN INTERACTING SYSTEMS OF SBS GALAXIES
A. FRANCO-BALDERAS, E. BEN~TEZAND J. A. DE DIEGO IA-UNAM, Apartado Postal 70-264, Mkxico DF-04510, Mkxico; alfred @astroscu.unam. mx We are carrying out a project for studying all the Second Byurakan Survey (SBS) interacting systems of galaxies at z < 0.1. The objectives of this project are: (1)t o link the histories of the star formation and nuclear activity in these systems with the morphologic type of the interacting galaxies; (2) to settle upper limits to the age of the induced starbursts using the Ha images, which relate with the dynamical time of the interaction; (3) to infer the mass of the stars which are crucial for understanding the physical properties of the perturbed interstellar medium.
1. Introduction It is well established that the mass distribution in each component of an interacting system of galaxies, and the connection between the timescales of the dynamical interaction and the starburst phenomenon, are important factors t o understand the result of the interaction [2]. B, R, and Ha images are necessary to infer the stellar population and the star formation rate in the interaction induced starbursts. Thus, we will determine the star formation histories and ages for each galaxy. As part of our observations, we present preliminary results for two of the systems that we have already observed. We follow the procedure described in [l]. 2. SBS 1241+551 AB
This is a system with a common luminous halo and an amorphous asymmetric structure visible in our B and R images. We see a low surface brightness tidal tail, and also a tenuous bridge between the two galaxies, that can be interpreted as a late interaction stage between them. Notice that, the south component of the system shows a complex internal structure. From our optical study, we can see that this galaxy posses two nuclei and shows a disrupted appearance.
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Figure 1. Left: B-band image of SBS1241+551 AB. Right: B-band image of SBS 1317+523 AB. Images were obtained a t San Pedro M k t i r Observatory (SPM) in the 1.5 m telescope with the 1024 x 1024 SI003 CCD.
3. SBS 1317+523 AB This is a system with a complex morphology. The northern component is a disrupted spiral galaxy with a prominent outer star formation ring. The southern component has been known as a Blue Compact Dwarf Galaxy (see NED), however, in our images it is not evident that this galaxy has an elliptical morphology. Surprisingly, we do not observe a common halo. 4. Future Work
Optical photometry and spectroscopy are planned for the complete sample of SBS interacting systems. This observations are planned with the 2.lm telescope in SPM, including high resolution (3D spectroscopy) with the PUMA instrument, which is a Fabry Perot attached to this telescope. Spectroscopic follow-up will be performed to study the chemical abundances. This information, along with an appropriate model for stellar population synthesis, will produce a better estimate for the mass of the starbursts. The spectroscopic data will also be used to study the dynamical properties and the large scale redistribution of the gas and the AGN activity.
References 1. A. Fkanco-Balderas, D. Dultzin-Hacyan, H.M. Hernhdez-Toledo & G. GarciaRuiz, A&A 406,415 (2003). 2. R.C. Kennicutt, K.A. Roettiger, W.C. Keel, J.M. van der Hulst & E. Hummel, A J 9 3 , 1011 (1987).
GOODS AGN HOST STRUCTURAL PARAMETERS AND ENVIRONMENT: EVIDENCE FOR BLACK HOLE-BULGE CORRELATION AND AGAINST MERGER-AGN CONNECTION AT 2 N 0.4-1.3
N. A. GROGIN Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles St., Baltimore, MD 81218, USA E-mail: nagroginopha.jhu. edu
C. J. CONSELICE Department of Astronomy, California Institute of Technology, 1201 East California Blvd., Pasadena, CA 91125, USA E-mail: ccaastro. caltech.edu E. CHATZICHRISTOU AND THE GOODS TEAM Department of Astronomy, Yale University, P. 0. Box 208101, New Haven, C T 06520-8101, USA E-mail: eleni. chatzichristouoyale.edu GO0DS Project URL : wwwstsci.edu/science/goods We investigate morphological structure parameters and local environments of distant AGN host galaxies in the overlap region between the HST/ACS observations of the Great Observatories Origins Deep Survey (GOODS/ACS) and the two Chandra Deep Fields. We compute asymmetry and concentration indices and near-neighbor counts for N 34000 GOODS/ACS galaxies, including N 350 X-ray-selected AGN hosts. Both the near-neighbor counts and the 2850 asymmetries of the 233 resolved, 2850 < 23 AGN host galaxies are consistent with the field values, implying no close connection between galaxy mergers and moderateluminosity AGN activity at appreciable lookback times ( z 5 1.3)approaching the epoch of peak AGN activity in the universe. The 2850 concentration indices for the AGN hosts are clearly skewed towards larger values; this 7a discrepancy is much larger than could be explained by the contribution of the nuclear point source to the hosts’ optical emission. From this we infer that the tight correlation observed locally between supermassive central black hole mass and host galaxy properties (including concentration index) persists to the substantial redshifts of our AGN and control samples. The multicolor GOODS/ACS imaging allows us t o track the comparative evolution of these morphological and environmental indicators in rest-frame B-band from J N 0.41.3 using volume-limited samples constructed from AGN redshifts in the literature and N 10000 GOODS/ACS field galaxy photometric redshifts. The J850 results
399
400 described above are separately reproduced within each of the three redshift intervals of the rest-frame B-band analysis.
This investigation of HST/ACS morphological indices (Figs. 1,2) and near-neighbor frequency of Chandra Deepest Field (CDF) AGNs represents a tenfold increase in sample size over the pilot study of Grogin et al. [l]. Please consult Grogin et al. [2] for the full description of the present work.
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Figure l.(left) Concentration index (top) and asymmetry index (bottom) versus magnitude as measured in 2850 for resolved GOODS sources. The large symbols represent the AGN sample in the north (squares) and south (triangles); the small dots represent the non-AGN in both fields. The bold crosses and error bars denote the median values and measurement errors for the non-AGN in successive 1-mag bins. Figure 2.(right) In three successive redshift bins (top to bottom), the cumulative distribution functions of rest-frame B-band concentration index (left panels) and asymmetry index (right panels) for a volume- limited sample of resolved, M B 5 -19.5 GOODS AGN hosts from the CDF-S (thick dotted), CDF-N (thick dashed), and the combination of both CDFs (thick solid). For comparison, we also plot the respective distributions for non-AGN GOODS-South galaxies with M B 5 -19.5 (thin solid).
References 1. N.A. Grogin et al., ApJ 595, 685 (2003). 2. N.A. Grogin et al., A p J submitted to Letters.
EXPLAINING LOW REDSHIFT QUASAR EVOLUTION
A. STEED AND D. H. WEINBERG The Ohio State University 140 West 18th Aue, Columbus, OH 43210, USA E-mail: asteed,
[email protected]. edu We have developed a flexible framework for constructing physical models of quasar evolution that can incorporate a wide variety of observational constraints, such as multi-wavelength quasar luminosity functions (QLFs), estimated masses and accretion rates of active black holes, space densities of quasar host galaxies, clustering measurements, and the mass function of black holes in the local universe. In this brief contribution we focus on the observed decline in the QLF break luminosity at t < 2, which can be explained either by a shift toward lower characteristic accretion rates at low z or by preferential suppression of activity in higher mass black holes.
The central actor in our treatment of quasar evolution (Steed & Weinberg 2004) is the accretion probability distribution p(ri-LIM,z ) , the probability that a black hole of mass M at redshift z is accreting mass at a rate riz in Eddington units. The key supporting players are the black hole mass function n ( M ,z ) and a physical model of accretion that predicts the radiative efficiency for a given m. At a given redshift, p(rizlM, z ) and n ( M ,z ) together determine the quasar luminosity function, and p(rizlM, z ) also determines the accretion driven growth of the black hole population, and hence the evolution of n ( M ,z ) . Boyle et al. (2000) find that the observed QLF at z < 2 is well described by a double power-law with a break luminosity, Lbrk, that declines toward low z. Since black hole masses themselves cannot decrease, we find that reproducing this behavior requires either a shift in p(7jZI.z) that increases the relative probability of low accretion rates or an evolving mass dependence of p(rizlM,z) that preferentially shuts off accretion onto high mass black holes at low z . With regard to @ ( L )alone, the two models are effectively degenerate. However, if the first mechanism dominates, then the QLF changes character between z = 2 and z = 0, shifting from a sequence of 40 1
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black hole mass toward a sequence of accretion rates. If the second method dominates, then the QLF remains a sequence of black hole mass at all redshifts, predicting that luminous AGN a t low redshift consist primarily of low mass black holes with a narrow range of m values that produce high L / L e d d . For details see Steed & Weinberg (2004).
log i n
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Figure 1. Alternative explanations for Boyle et al.’s (2000) observed luminosity evolution (points in the right hand panels). Upper panels show a model in which p ( h , z ) is independent of mass but evolves to lower characteristic m. Lower panels show a model in which the shape of p ( m ) is fixed but the mass-dependent normalization p r ( M ) evolves, preferentially reducing the duty cycle of high mass black holes at low redshifts.
References 1. B.J. Boyle, T. Shanks, S.M. Croom, R.J. Smith, L. Miller, N. Loaring & C. Heymans, M N R A S 317,1014 (2000). 2. A. Steed & D.H. Weinberg, A p J submitted (2004) (astro-ph/0311312).
DETERMINATION OF NUCLEAR SB AGES IN SEYFERT GALAXIES
J.P. TORRES-PAPAQUI, R. TERLEVICH AND E. TERLEVICH Instituto Nacional de Astrofisica, Optica y Electrdnica, Luis Enrique Err0 1, Tonantzintla, Puebla 72840, Mexico E-mail:
[email protected] We have obtained optical-near UV spectra of nuclear regions of Seyfert galaxies over the wavelength region 3600-5300 A. We find that many Seyferts, both type 1 and type 2 show the high-order Balmer lines in absorption. The detection of these Balmer absorptions constitute a strong evidence of the presence of recent star formation in the nuclear region of these active galaxies. While this finding supports some kind of connection between starburst and AGN activity it is not yet clear that starburts are present in all AGNs and what ages do they have. If such a connection exists, it would bear important implications for theories of AGN formation and their role in galaxy formation and evolution. We present a new method to determine ages of the stellar populations in the nuclei of Seyfert galaxies where dilution plays a major role. Our method is based on the comparison of the profiles of the high-order Balmer and Ca K absorption lines with our high spectral resolution synthesis models. The profile comparison method is insensitive to the dilution that affects the traditional spectral analysis methods.
1. Guidelines 1.1. The Database
Our database consists of spectra of nearby Seyfert galaxies taken by us at the 2.12m telescope of the OAGH (Cananea, Mexico) and at the 3.5m ESO NTT. The sample was selected from Veron-Cetty and Veron (2000) and from Nelson and Whittle (1995) catalogs.
1.2. Discussion The dilution makes use of traditional methods based on absorption line strength, extremely difficult or impossible to use. We have developed an alternative method that uses the profile of those absorption lines whose main broadening mechanism is related to the surface gravity of the stars. The hydrogen Balmer series and the CaII H and K lines are excellent ex403
404
amples of this effect. Both sets of lines becoming increasingly broad as the stellar population ages. Within our observed spectral range the main characteristic of recent star formation are strong emission lines plus Balmer absorptions while strong Ca I1 absorption is typical of the older bulge population. The new method was calibrated using population synthesis models combining two different age stellar populations. (1) a young population with age ranging from lo7.' to 108.6yrs, representing a starburst compoyrs, nent, and (2) an old population with age ranging from lo8.' to representing the bulge component. 1.3. Results
The results of applying the method to our sample of Seyfert galaxies and the Solar abundance synthesis models is that the stellar populations are young but not extremely so with ages ranging from 40 to 500 Myrs in the Balrner estimator, i.e. the starburst component, and from 400 to 4000 Myr in the CaII estimator, i.e. the bulge component. The age shift reflects the difference in the mean ages of the central starforming region and the older galaxy bulge. Globally, there seems to be a systematic shift between type 1 and type 2 Seyferts, with the type 1 having shorter ages than the type 2. 1.4. Conclusions
The main contribution of this work is the finding of direct evidence for massive star formation in the central regions of type 1 Seyfert galaxies and its confirmation in type 2 Seyferts. We postulate that it is posible to determine the age of the nuclear stellar population in these galaxies using new methods that are insensitive to the presence of a diluting nuclear continuum and/or the effects of reddenning. Applying the new method we find a systematic difference in the age of the nuclear stellar populations between type 1 and type 2 Seyferts. The type 1 Seyferts seem to be systematically younger than the type 2. References 1. C.H. Nelson & M. Whittle, ApJS 99, 67 (1995). 2. M.P. Veron-Cetty & P. Veron, Vizier On-line Data Catalog VII/215, (2000).
AGN and Large Scale Structures
406
Roberto Gilli, Marco Chiaberge and Sergio Mendoza
LARGE-SCALE STRUCTURES IN THE CHANDRA DEEP FIELDS
R. GILL1 I N A F - Osseruatorio Astrofisico d i Arcetri Largo E. Fermi 5, 50125 Firenze, Italy E-mail: gilliQarcetri. astro.it The redshift distribution of the X-ray sources identified so far in the Chandm Deep Field South (CDFS) is characterized by several spikes, the most prominent of which are at z = 0.67 and z = 0.73. The clustering properties of the CDFS sources (mainly AGN) and, for comparison, those of the X-ray selected AGN in the 2 Msec Chandm Deep Field North (CDFN) have been measured via the projected correlation function w ( r p ) .The AGN clustering amplitude is found to be a factor 2 higher in the CDFS than in the CDFN, revealing large cosmic variance in of these 0.1 deg2 fields. The high (5 - 10 h-' Mpc) correlation length measured for AGN at z N 1 in the two Chandra Msec fields is comparable to that of early type galaxies at the same redshift. N
1. Introduction Active Galactic Nuclei (AGN) are one of the best tools t o study the large scale structure of the Universe a t intermediate-high redshifts, z 1 - 2, i.e. at an epoch where matter was undergoing the transition from the initially smooth state observed at the recombination to the clumpy distribution observed at present time 18. The AGN spatial clustering has been directly measured by means of optical surveys encompassing an increasing number of QSO , but in the X-ray band, where the bulk of the obscured AGN population should emerge this is still poorly constrained. Significant clustering signal in the X-rays has been detected from angular correlations which have been often converted into spatial correlations by assuming an a pn'on' redshift distribution. Unfortunately, because of the several uncertainties in its assumptions, this method has not provided stringent results. To date, the only direct measurement of the spatial correlation function of X-ray selected AGN, usually approximated by a powerlaw ( ( r ) = ( T - / T - o ) - ~ has , been obtained by Mullis 22, who found TO = 6.8 f 1.6 h-' Mpc for the AGN in the ROSAT NEP survey (the N
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slope was fixed t o y = 1.8). Because of the short exposure times and the ROSAT limited sensitivity only bright sources, with a surface density of N 3 degP2, were detected in the NEP survey. Since the spatial correlation function is a power law increasing at lower pair separations, deep pencil beam surveys like the lMsec Chandra Deep Field South (CDFS 23,12) and where the X-ray source the 2Msec Chandra Deep Field North (CDFN surface density is about 3000 - 4000 deg-', are expected to provide the highest signal significance with the minimum number of identified objects. '13),
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Figure 1. Left: Redshift distribution for CDFS sources in bins of Az = 0.02. The solid curve shows the smoothed distribution used to calculate w(rP)(see text). The inset shows the redshift distribution for different source classes. Right: Same as in the left panel but for CDFN sources.
2. Large scale structures in the
CDFS
In the lMsec ACIS-I observation of the CDFS a total of 346 X-ray sources have been detected over the whole 0.1 deg2 field 23,12. In the center of erg cm-2 erg cm-2 s-l and 4.5 the field limiting fluxes of 5.5 s-l have been achieved in the 0.5-2 keV (soft) and 2-10 keV (hard) band, respectively. So far 127 high quality redshifts with two or more identified lines (N 35% of the total sample) have been obtained by means of VLT spectroscopy 25. The spectroscopic completeness increases to 78% when considering X-ray sources with optical counterparts brighter than R = 24. As shown in Fig. 1 (left) the redshift distribution is dominated by two large concentrations of sources at z = 0.67 and z = 0.73, while other
409
RA (J2wO)Id&
Figure 2. Left: Chandra ACIS-I image of the CDFS with X-ray sources at z = 0.67 and z = 0.73 marked with circles and squares, respectively. Extended sources are represented as big symbols. The dashed box indicates the region covered by the K20 survey 5 . Right: 60 x 60 arcsec R band image of the extended X-ray source XID 594 with X-ray contours overlaid 2 5 . Four identified objects at z = 0.73 are marked with squares.
smaller peaks are also visible 14. The distribution on the sky of the sources in the two spikes is shown in Fig. 2 (left). A few of them are extended in the X-rays (one is shown in Fig. 2 (right)), corresponding to galaxy groups/clusters embedded in larger structures, thus providing a beautiful sketch of the cosmic web. About 1/10 of the X-ray field has been covered by the K20 near-infrared survey Similarly to the X-ray data, the redshift distribution of the galaxies identified in the K20 survey has two prominent peaks at z = 0.67 and z = 0.73. Moreover, at z < 1.3, where the K20 survey is more sensitive, there is almost a one-to-one correspondence between less prominent X-ray and K20 redshift spikes 14.
'.
3. The spatial correlation function in the CDFS and CDFN Gilli et al. l5 measured quantitatively the clustering level of CDFS sources by means of the projected correlation function w ( r p ) lo. For comparison w ( r p )was also calculated for the N 250 X-ray sources with robust spectroscopic redshift identified so far in the CDFN '. The redshift distribution for the considered CDFN sample is shown in Fig. 1 (right). As in the case of the CDFS redshift distribution, several spikes, although less prominent than those of the CDFS, can be immediately recognized '. To measure the clustering properties of different source populations, the X-ray hardness ra-
410
tio vs. X-ray luminosity diagram presented by Szokoly et al. 25 was used to classify the X-rays sources as type-1 AGN, type-2 AGN and galaxies. a The spatial correlation function essentially measures the excess of source pairs at a given separation with respect to a random distribution. To avoid distortions due to peculiar velocities, the spatial clustering of CDFS and CDFN sources was estimated by means of the projected correlation function w ( r p )lo which can be easily related to the real-space correlation function. The minimum variance estimator proposed by Landy & Szalay l9 was used, and special care was taken in creating the random control sample 15. In particular the objects in the random sample were placed at the coordinates of the real sources, and their redshifts were extracted from a smoothed distribution of the observed one. This procedure was extensively tested and found to be appropriate for the CDFS and CDFN samples 15. The projected correlation function w ( ~ - was ~ ) measured at different scales rP and the best fit parameters y and TO were determined via x2 minimization. We note that while Poisson errorbars underestimate the true uncertainties on the TO and y values when the source pairs are not independent, bootstrap resampling techniques 21, which are often used to circumvent this problem, may substantially overestimate the real uncertainties (for our samples bootstrap errors are a factor of 2 larger than Poissonian errors 1 5 ) . In the following we will simply quote TO and y together with their la Poisson errors, bearing in mind that the most likely uncertainty lay between the quoted number and its double. A flat cosmology with s1, = 0.3 and Cl* = 0.7 is assumed; comoving distances in units of h-' Mpc are quoted, where HO= 100 h km s-'. N
3.1. Results
Both in the CDFS and CDFN the clustering level of the total X-ray samples is dominated by that of AGN, which indeed represents the majority of the identified sources. In both fields the correlation function is measured on scales rP = 0.16 - 20 h-' Mpc for AGN at a median redshift of z 0.9 and with median X-ray luminosity of LO.5-10 erg s-l, i.e. in the Seyfert luminosity regime. The best fit parameters of the AGN correlation function were found to be TO = 10.3 f 1.7 h-' Mpc, y = 1.33 f 0.14 in the CDFS and TO = 5.5 f 0.6 h-' Mpc, y = 1.50 f 0.12 in the CDFN. As verified by Gilli et al. 1 5 , the difference in the TO values between the two
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aThat scheme was somewhat simplified by avoiding the luminosity distinction between type-:! AGN/QSOs and between type-1 AGN/QSOs.
41 1
Figure 1. left: continum substrace spectra of the Qsos in our sample Figure 1. left: continum substrace spectra of the Qsos in our sample
1
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fields is not due to observational biases affecting in different ways the two samples (i.e. different X-ray sensitivity or spectroscopic incompleteness), but is rather due to genuine cosmic variance. Indeed, while in the CDFS about 1/3 of the identified sources lay within the two spikes at z = 0.67 and z = 0.73, no such prominent features are observed in the CDFN (for comparison two most populated spikes of the CDFN contain only 1/8 of the identified sources). When excluding the sources in the two redshift spikes at z = 0.67 and z = 0.73, the correlation length measured for CDFS AGN is found to be in excellent agreement with that measured in the CDFN. The slope of the correlation, y = 1.3- 1.5, is flatter than that commonly observed for galaxies (y 1.6 - 2.0 but is consistent within the errors with the value of y = 1.56f0.10 measured for the sample of > lo4 optically selected QSO in the 2QZ survey '. We note that, when fixing the slope of the correlation to y = 1.8 the best fit TO values measured in the CDFS and in the CDFN increase by only 15%. Within each field no significant clustering differences are found between soft and hard X-ray selected sources, or, similarly, between type-1 and type-2 AGN. The good correspondence between the redshift peaks of X-ray and Kband selected sources in the CDFS l 4 supports the idea that Seyfert-like AGN clustering is similar to that of early type galaxies, whose detection rate is higher in K-band rather than in optically selected samples. In the CDFS this is indeed directly confirmed, since the measured TO value is similar to that of Extremely Red Objects (i.e. galaxies with R - K > 5) a t z 1, which are thought to be the progenitors of early type galaxies '. When considering the lower amplitude observed in the CDFN, we can estimate N
20717)
N
41 2 the correlation length of the AGN in the Chundru Msec fields t o be in the range 5 - 10 h-' Mpc, which this is still consistent with Seyfert-like AGN at z 1 t o be generally hosted by early type galaxies (Coil e t al. found rg = 5.5 - 7.7 h-l Mpc and rg = 2.6 - 3.7 h-I Mpc for early and late type 1, respectively). galaxies at z
-
N
Acknowledgments All this work has been performed in collaboration with many people in the CDFS and K20 team who I gratefully acknowledge: E. Daddi, G. Zamorani, P. Tozzi, S. Borgani, J. Bergeron, R. Giacconi, G. Hasinger, V. Mainieri, C. Norman, P. Rosati, G. Szokoly, W. Zheng, A. Cimatti, L. Kewley, M. Nonino, J.X. Wang, M. Mignoli, A. Zirm. I wish t o thank Raul Mujica and Roberto Maiolino for their patience in waiting for this contribution.
References 1. D.M. Alexander et al., AJ 1 2 6 , 539 (2003). 2. A. Akylas, I. Georgantopoulos & M. Plionis, MNRAS 3 1 8 , 1036 (2000). 3. A.J. Barger et al., AJ 1 2 6 , 632 (2003). 4. S. Basilakos et al., ApJL in press, (2004). (astro-ph/0404413) 5. A. Cimatti et al., A B A 3 9 2 , 395 (2002). 6. A.L. Coil et al., ApJ in press, (2004). (astro-ph/0305586) 7. A. Comastri, G. Setti, G. Zamorani & G. Hasinger, A&A 2 9 6 , 1 (1995). 8. S.M. Croom et al., MNRAS 3 2 5 , 483 (2001). 9. E. Daddi et al., A B A 3 7 6 , 825 (2001). 10. M. Davis & P.J.E. Peebles, ApJ 2 6 7 , 465 (1983). 11. R. Giacconi et al., A p J 5 5 1 , 624 (2001). 12. R. Giacconi et al., ApJS 1 3 9 , 369 (2002). 13. R. Gilli, M. Salvati & G. Hasinger, AtYA 3 6 6 , 407 (2001). 14. R. Gilli et al., A p J 5 9 2 , 721 (2003). 15. R. Gilli et al., A&A submitted, (2004). 16. A. Grazian et al., AJ 1 2 7 , 592 (2004). 17. L. Guzzo et al., A p J 4 8 9 , 37 (1997). 18. F.D.A. Hartwick & D. Schade, A R A B A bf 28, 437 (1990). 19. S.D. Landy & A.S. Szalay, ApJ 4 1 2 , 64 (1993). 20. 0. Le Fevre et al., A p J 4 6 1 , 534 (1996). 21. H. J. Mo, Y. P. Jing & G. Borner, ApJ 3 9 2 , 452 (1992). 22. C.R. Mullis, Ph.D. thesis, University of Hawaii (2001). 23. P. Rosati et al., ApJ 5 6 6 , 667 (2002). 24. T. Shanks et al., MNRAS 2 7 7 , 739 (1987). 25. G. Szokoly et al., ApJS submitted, (2004). (astro-ph/0312324) 26. A. Vikhlinin & W. Forman, A p J 4 5 5 , L109 (1995). 27. Y. Yang et al., ApJ 5 8 5 , L85 (2003).
NEW RESULTS ON THE AGN POPULATION IN CLUSTERS OF GALAXIES
P. MARTINI
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS20, Cambridge, M A 02138, USA E-mail: pmartiniQcfa.harvard. edu D. D. KELSON, J. S. MULCHAEY AND A. ATHEY Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101, USA E-mail:
[email protected],
[email protected],
[email protected] We have analyzed archival Chandra observations of ten low-redshift ( z < 0.3) clusters of galaxies to identify AGN in cluster members. Spectroscopy of X-ray sources with optically-bright counterparts reveals that a significant fraction are cluster members and suggests the fraction of AGN in bright cluster galaxies is 5%. The fraction of AGN in any given cluster, however, appears to vary considerably from cluster to cluster and may depend on a cluster's properties. The host galaxy population in clusters also varies significantly, ranging from galaxies dominated by old stellar populations in some clusters, to starforming and poststarburst populations in others. N
1. Introduction The ingredients for black hole accretion and star formation are qualitatively similar: a cold gas supply and mechanism for angular momentum loss. The comparable space density evolution of luminous quasars and starburst galaxies supports this simple scenario, although these processes differ in detail and this is reflected by the absence of a perfect correlation. Clusters of galaxies offer a distinct astrophysical laboratory in which to test models of the connection between AGN and star formation, and thus models of galaxy evolution, because of the extremely stark evolution in the star formation rate and morphologies of cluster galaxies since z 0.5, relative to the field galaxy population.'>2
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The physical mechanisms invoked to explain this rapid galaxy evolution in clusters include both hydrodynamical effects, such as ram-pressure tripping,^ and gravitational effects, such as mergers or interactions between g a l a ~ i e sIf. ~the cluster environment has a similar impact on nuclear accretion, then there should be significant evolution in the fraction of AGN in clusters. However, few AGN have been identified in large, spectroscopic ~ is likely due to the signifisurveys of the cluster galaxy p ~ p u l a t i o n .This cant dilution of AGN emission-line diagnostics by host galaxy starlight and obscuration by high column density material.6 X-ray selection is a much more efficient and unbiased method for identifying AGN in clusters. This result is supported by a preliminary study of Abell 2104 ( z = 0.15), which revealed five times as many AGN as expected from previous work.6 2. Survey Overview
We have identified a sample of ten clusters at 0.05 < z < 0.3 with sufficient archival Chandru data to reach a typical limiting sensitivity of Lx[2 10lceVI 2 104’erg s-l. The Chandru data are vital to this program, as they enable relatively unbiased and highly efficient identification of AGN: the luminous, hard X-ray source population is dominated by AGN, whereas obvious AGN are apparent in only a small minority of galaxies with (low signal-to-noise) spectroscopy at visible wavelengths. This low-redshift range was selected to study AGN in relatively “nearby” clusters, a sample which will serve as a necessary point of comparison for future, high-redshift studies of AGN evolution in clusters. Below z 0.05 the projected size of the Chundra ACIS-I field of view is much smaller than the spatial extent of typical clusters of galaxies. We identified optically-bright counterparts to all of the X-ray sources in the fields of these clusters with BVRI photometry obtained with the 2.5m du Pont telescope and WFCCD at Las Campanas Observatory. Multislit spectroscopy with LDSS2 on the 6.5m Magellan telescopes was then obtained to determine redshifts for these X-ray sources, as well as membership data for other cluster galaxies. Illustrative color-magnitude diagrams and spectra are shown in Figures 1 and 2. N
3. Preliminary Results
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Our main result to date is that AGN are present in 5% of bright cluster galaxies at z < 0.3. These cluster AGN reside in the full range of galaxy populations found in clusters, including starforming galaxies, post-
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R [mag1 Figure 1. (B - R) - R Color-magnitude diagrams for four clusters observed in March 2003. Each panel shows all of the photometric data for the cluster field (points), counterparts to the X-ray sources (open circles), and confirmed cluster members (large, filZed circles).
starbursts, and those dominated by old stellar systems (see Figure 2).7 We also find a significant variation in the number of AGN from cluster to cluster and that the number of AGN found in a given cluster depends on cluster properties, such as dynamical state. These results show that there are sufficient numbers of AGN in clusters of galaxies for statistical studies, particularly the evolution in the AGN cluster population with redshift, that hold great promise for investigation of the evolution of AGN and galaxies in the cluster environment.
41 6
Figure 2. Spectra of four luminous, X-ray sources in AC 114. These spectra illustrate the wide range of host galaxy types found in cluster AGN, including a galaxy with some star formation (#1172), a poststarburst galaxy (#616), and two galaxies dominated by an old stellar population (#554, #449).
Acknowledgments Support for this work was provided by the National Aeronautics and Space Administration through Chandra Award number 4700793, issued by the Chandra X-Ray Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS 8-39073
References B.M. Poggianti et al., ApJ 518,576 (1999). A. Dressler et al., ApJS 122, 51 (1999). J.E. Gunn& J.R.I. Gott, ApJ176, l(1972). J.S. Gallagher I11 & J.P. Ostriker, ApJ 77, 288 (1972). A. Dressler, I.B. Thompson & S.A. Shectman, ApJ 488, 481 (1985). P. Martini, D.D. Kelson, J.S. Mulchaey & S.C. Trager, ApJ 576, L109 (2002). 7. P. Martini, D.D. Kelson, J.S. Mulchaey & A. Athey, in Carnegie Observatories Astrophysics Series, Vol. 3: Clusters of Galaxies: Probes of Cosmological Structure and Galaxy Evolution, ed. J. S . Mulchaey, A. Dressler & A. Oemler (Cambridge: Cambridge Univ. Press) (2004).
1. 2. 3. 4. 5. 6.
THE TRIGGERING AND BIAS OF RADIO GALAXIES
K. BRAND National Optical Astronomy Observatory, Tucson, A Z 85726-6732 E-mail:
[email protected] S. RAWLINGS Astrophysics,Department of Physics, Keble Road, Oxford, OX1 3RH
J. TUFTS AND G. J. HILL McDonald Observatory and Department of Astronomy, University of Texas at Austin, RLM 15.308, Austin, T X 78712 We present new results on the clustering and three-dimensional distribution of radio galaxies from the Texas-Oxford NVSS Structure (TONS) survey. The TONS survey was constructed to look at the distribution of radio galaxies in a region of moderate (0 5 z 5 0.5) redshifts by matching NVSS sources with objects in APM catalogues to obtain a sample of optically bright (R 5 19.5), radio faint (1.4-GHz flux density S1.4 2 3 mJy) radio galaxies over large areas on the sky. We find that redshift spikes, which represent large concentrations of radio galaxies which trace (= 100 Mpc3) super-structures are a common phenomena in these surveys. Under the assumption of quasi-linear structure formation theory and a canonical radio galaxy bias, the structures represent x 4-5a peaks in the primordial density field and their expected number is low. The most plausible explanation for these low probabilities is an increase in the radio galaxy bias with redshift. To investigate potential mechanisms which have triggered the radio activity in these galaxies and hence may account for an increase in the bias of this population, we performed imaging studies of the cluster environment of the radio galaxies in super-structure regions. Preliminary results show that these radio galaxies may reside preferentially at the edges of rich clusters. If radio galaxies are preferentially triggered as they fall towards rich clusters then they would effectively adopt the cluster bias.
1. Introduction Radio galaxies are ideal probes of large-scale structure as they are biased tracers of the underlying mass and can be easily detected out to high redshifts. By using biased galaxies populations, one can efficiently trace huge super-structures (i.e. clusters of clusters of galaxies) which are still in the 41 7
41 8
linear regime and can therefore be directly traced back to rare fluctuations in the initial density field at recombination. However, in order to be useful probes, it is vital to understand how different populations of radio galaxies trace the underlying dark matter (i.e. their bias) and how this has evolved with time. This is directly related to how the radio activity is triggered in different populations and in different environments. 2. The TONS survey
The Texas-Oxford NVSS Structure (TONS) survey is a radio galaxy redshift survey comprising three ( w 25 deg2) independent regions on the sky selected in the same areas as the 7CRS6 and the TexOx-1000 (TOOT) survey3. Unlike 7CRS or TOOT, the TONS survey is selected at 1.4 GHz from the NVSS survey and has fainter radio flux density limits. It also has an optical magnitude limit imposed on it and hence is optimized for looking at clustering of radio galaxies at moderate redshifts ( z 5 0.5). We obtained optical spectra for all the 84 and 107 radio galaxies in the TONS08 and TONS12 sub-regions respectively. Full details on the the survey selection and observations can be found in ’. 3. Super-structures as traced by radio galaxies
Fig. 1 shows the redshift distributions of the TONS08 and TONS12 subsamples. Two significant redshift spikes can been seen at z x0.27 and z x0.35 in the TONS08 sub-sample and z x0.24 and z ~ 0 . 3 2in the TONS12 sub-sample. It appears that redshift spikes are a common phenomena in this radio galaxy population. These redshift spikes correspond to huge ( x 100 Mpc3) super-structures. Assuming the canonical radio galaxy bias4, structure formation theories1 predict far fewer super-structures of this size and overdensity than are observed in the TONS survey. The easiest way to reconcile this result is if the radio galaxy bias of this population is larger than the canonical local value. 4. The cluster environment of radio galaxies
Comparing the richness of the environment of the TONS radio galaxies within super-structure regions to those of other radio galaxies should determine whether the large-scale environment is important for triggering of radio activity. For example, the cluster environment may influence the frequency of mergers and interactions between galaxies which may provide fuel
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to re-ignite the radio emission from the central black hole. Any increase in the triggering of radio activity in dense environments will manifest itself as an increase in the bias of the population. R-band imaging of all 27 radio galaxies in the z=0.27 super-structure in TONS08 survey was performed on the Imaging Grism Instrument (IGI) mounted on the 2.7m Harlan J. Smith telescope at the McDonald Observatory, Texas. We find that the radio galaxies in the TONS08 super-structure are generally in moderately rich (Abell class 0) environments. In addition, R-band imaging has been performed over the entire TONS08 region using the Prime Focus Corrector (PFC) on the 0.8m telescope at McDonald observatory. Clusters are detected using a matched filter technique5. Fig. 2 shows the spatial distribution of the cluster candidates and the z=0.27 and z=0.35 TONS08 super-structure members. All radio galaxies in rich (Brg>732) environments are within a projected distance of 2.3 Mpc of a cluster candidate. For the z=0.27 super-structure, 63 per cent of the radio galaxies are within 3 Mpc (assuming they are at the same redshift) of a cluster candidate. Preliminary results show that in all cases where we have the redshift measurements of cluster candidates near a TONS08 radio galaxy, the redshifts are the same. 5 . Discussion
The TONS08 radio galaxies within super-structure regions are generally in moderately rich (Abell class 0) environments. However, 63 per cent of the radio galaxies are within a projected distance of 3 Mpc from the centre of
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Figure 2. An RA versus DEC plot showing the spatial positions on the sky of the TONS08 z=0.27 (left) and z=0.35 (right) super-structure radio galaxies with rich (solid stars) and poorer (empty stars) environments. Solid circles show the spatial positions of cluster candidates. The line in the bottom right-hand corner represents the angular size that a length scale of 3 Mpc at z=0.27 would have on the sky.
a cluster candidate. The fact that we see so many radio galaxies near rich clusters suggests that the radio galaxies are associated with rich clusters but often only on the edges of high overdensity regions. This explains why we find that the radio galaxies are only in moderately rich environments: many of the radio galaxies are further than 0.5 Mpc from the cluster centre. One possible scenario is that of radio galaxies a t the centres of poor groups of galaxies being preferentially triggered as the group falls down large-scale structure filaments towards rich clusters. The radio galaxies would then effectively adopt the cluster bias, and the number of redshift spikes we see in the data would become consistent with the number that we expect.
This material is based in part upon work supported by the Texas Advanced Research Program under Grant No. 009658-0710-1999. References 1. J.M. Bardeen, J.R. Bond, N. Kaiser & A S . Szalay, ApJ 304,15 (1986). 2 . K.Brand, S. Rawlings, G. 3. Hill, M. Lacy, E. Mitchell & 3. Tufts, MNRAS 344,283 (2003). 3. G.J. Hill & S. Rawlings, NewAR 47,373 (2003). 4. J.A. Peacock & D. Nicholson, MNRAS 253, 307 (1991). 5 . M. Postman et al., A J 111,615 (1996). 6. C. J. Willott, S. Rawlings, K.M. Blundell, M. Lacy, G.J. Hill & S.E. Scott, MNRAS 335,1120 (2002).
AGN ACTIVITY IN HIGH REDSHIFT CLUSTERS AND PROTOCLUSTERS
0. JOHNSON AND P. BEST Institute for Astronomy Royal Observatory Edinburgh Blackford Hill Edinburgh EH9 3HJ, UK E-mail:
[email protected] 0. ALMAINI School of Physics and Astronomy University of Nottingham University Park Nottingham NG7 2RD, UK
We discuss a Chandra observation of the z = 0.83 cluster MS1054 and identify an excess of point sources in this field likely to be luminous AGN populating the outskirts of the cluster. We also report first results from an extremely deep XMM survey of the SSA22 protocluster field at z = 3.09.
1. Introduction Chandra’s unprecedented resolution and high sensitivity over the full X-ray band, in conjunction with multi-scale wavelet detection techniques which reliably separate small-scale point source emission from surrounding diffuse emission (e.g., Freeman et al. 2002), have allowed the first detailed X-ray surveys of AGN within cluster environments. Surveying AGN within these dense regions a t high redshift allows investigation of the interplay between AGN, their hosts, and the intracluster medium within forming clusters. In this contribution we present two studies, one of an X-ray luminous massive cluster at z = 0.83 and one of a complex protocluster region at z = 3.09. This work is part of an ongoing project a t Edinburgh to study the AGN content of a large number of high redshift clusters and protoclusters (see Dowsett et al., this volume). 42 1
422
2. MS1054-03:A massive cluster at z
= 0.83
At t = 0.83, MS1054-03 is the most distant cluster in the Einstein Medium Sensitivity Survey of X-ray selected clusters, with a diffuse luminosity of L X = 1.2 x 1045h-2 erg s-l (Gioia et al. 1990). It is a rich (Abell class 3), dynamically young cluster showing substantial substructure (Hoekstra, Frank, & Kuikjen 2000) and a high merging fraction (van Dokkum et al. 2000). Extemely deep radio observations at 5 GHz reveal at least 6 radio AGN hosted by cluster members (Best et al. 2002).
Figure 1. A Chandm image of MS1054-03 reveals luminous AGN likelv associated with the cluster (bold circles) at radii of 1 - 2 Mpc from the cluster core. Less luminous
radio AGN (diamonds) are detected nearer to the center. Figure from Johnson, Best, & Almaini (2003).
Using a 91 ksec archival Chandra observation first presented in Jeltema et al. (2001), we have conducted a survey of X-ray point sources in the MS1054-03 field. In Johnson, Best, & Almaini (2003), we show evidence for a significant excess of sources which are likely luminous AGN associated with the cluster. Two of these sources have already been spectroscopically confirmed, and further observations are ongoing. This result and others (e.g., Cappi et al. 2001; Martini et al. 2002; Pentericci et al. 2002) indicate that increasingly luminous cluster AGN are seen toward higher redshift.
423
However, not all clusters at high redshift contain AGN, suggesting other factors, such as dynamic state and cluster richness, may regulate AGN activity in high density regions. We also report preliminary but intriguing evidence that luminous AGN are found preferentially at the edges of the cluster, with fainter radio AGN or starbursts detected nearer the core, as illustrated in Figure 1. This is potentially an extremely significant finding, as it speaks to the debate of whether the dense cluster environment serves only to quench starburst/AGN activity through tidal and/or ram pressure stripping of the galaxy’s gas, or whether introduction to that environment first triggers activity through compression and shocks. If the latter scenario is correct, luminous cluster AGN may be expected to be hosted predominantly in galaxies just joining the cluster environment - as appears to be the case in MS1054-03, as well as in A2104 (Martini et al. 2002). In this context, the less luminous sources detected nearer the center of MS1054-03 in sensitive 5 GHz observations may illustrate decreased activity in galaxies which have been longer resident in the cluster environment. Study of the AGN content of a larger sample of clusters is clearly needed to investigate this issue further.
3. SSA22: A protocluster region at z = 3.09 Discovered as a ‘spike’ in redshift space in a Ly-break survey (Steidel et al. 1998), the galaxy overdensity in the SSA22 field now has over 100 identified members in a region of 10 by 14 comoving Mpc, and is almost certainly the precursor to a bright X-ray cluster. Multiwavelength observations have identified a complex variety of sources associated with the forming cluster. Deep Lya imaging reveals, in addition to faint protocluster member candidates, two diffuse blobs of emission with Lya luminosity of erg s-l and physical sizes of 100 kpc (Steidel et al. 2000). These features have also been detected in the submillimeter, along with an overdensity of SCUBA sources some of which are associated with the protocluster (Chapman et al. 2001; Chapman and Baugh 2004). A recent optical spectroscopic study of one of these blobs finds that the kinematics of the emission are suggestive of a large-scale galactic outflow resulting from an extreme starburst (Ohyama et al. 2003), while another study finds multiwavelength data consistent with a dust-obscured AGN within a starburst embedded in the Lya cloud (Chapman et al. 2003). However, there is no evidence in a 70 ksec Chandra exposure of X-ray emission associated with this object. N
N
424
We present first results of an analysis of an extremely deep (150 ksec) XMM exposure of the region. This is the deepest X-ray view of a known rich protocluster region, and the high sensitivity achieved, particularly in the hard band, places strong limits on diffuse and point source emission in this system. Preliminary analysis reveals no evidence of diffuse X-ray emission assoerg s-’. There is ciated with the cluster to a diffuse flux limit of similarly no evidence of an ionizing source for the diffuse Lya blobs in the X-ray, which favors the starburst interpretation described above. Over 150 X-ray point sources are detected over the XMM FOV, to point souce limits of 1 x erg s-l cmP2 with the two MOS cameras erg s-l cm-2 with the P N detector. The direct detection and 5 x rate of protocluster members is low. At most four of the 19 Ly-break objects within the redshift ‘spike ’ are detected in the X-ray, and none of the SCUBA sources in the field is individually detected. Extended Lya narrowband imaging extends the number of Lya excess and deficit sources likely associated with the protocluster to N 180. At most five of these objects are directly detected in the X-ray. A stacking analysis is underway to put ensemble limits on the X-ray emission of the high redshift populations in this field. N
References P. Best et al., MNRAS 330, 17 (2000). M. Cappi et al.,ApJ 548, 624 (2001). S. Chapman et al., ApJ 548, L17 (2001). S. Chapman et al., astrc-ph/0310670 (2003). S. Chapman & C. Baugh, in Carnegie Observatories Astrophysics Series, Vol. 3: Clusters of Galaxies: Probes of Cosmological Structure and Galaxy Evolution, ed. J. S . Muchaey, A. Dressler, and A. Oemler (2004). 6. P.E. Freeman et al., ApJS 138, 185 (2002). 7. I.M. Gioia et al., ApJS 7 2 , 567 (1990). 8. H. Hoekstra, M. Franx & K. Kuijken, A p J 532, 88 (2000). 9. T.E. Jeltema et al., ApJ 562, 124 (2001). 10. 0. Johnson, P. Best & 0. Almaini, MNRAS 343, 924 (2003). 11. P. Martini et al., ApJ 576, 109 (2002). 12. Y . Ohyama et al., ApJ 591, 90 (2003). 13. L. Pentericci et al., A&A 396, 109 (2002). 14. C. Steidel et al. ApJ492, 428 (1998). 15. C. Steidel et al., ApJ532, 170 (2000). 16. P.G. van Dokkum et al., ApJ 541, 95 (2000).
1. 2. 3. 4. 5.
THE CLUSTGRING OF XMM-NEWTON HARD X-RAY SOURCES
M. P L I O N I S ~* ~s. ~ BASILAKOS~,A. GEORGAKAKIS~AND I. GEORGANTOPOULOS~ Instituto Nacional de Astrofisica, Optica y Electronica, Puebla, Mexico I A A - National Observatory of Athens, Greece
We present the clustering properties of hard (2-8 keV) X-ray selected sources deergcm-2s-1] tected in a wide field (% 2deg2) shallow [fx(2 - 8keV) = and contiguous XMM-Newton survey. We perform an angular correlation function analysis using a total of 171 sources to the "boy: flux limit. We detect a N 4a correlation signal out to 300arcsec with w(O < 300 ) N 0.13f0.03. Modeling the two we find: point correlation function as a power law of the form w(0) = (Oo/O)T-l B0 = 48.9:;:; arcsec and y = 2.2 f 0.30. Fixing the correlation function slope to y = 1.8 we obtain = 22.22::; arcsec. Using Limber's integral equation and a variety of possible luminosity functions of the hard X-ray population, we find a relatively large correlation length, ranging from r0 9 to 19 h-l Mpc (for y = 1.8 and the concordance cosmological model), with this range reflecting also different evolutionary models for the source luminosities and clustering characteristics. N
1. Introduction
The overall knowledge of the AGN clustering using X-ray data comes mostly from the soft X-ray band (Boyle & Mo 1993; Vikhlinin & Forman 1995; Carrera et al. 1998; Akylas, Georgantopoulos & Plionis 2000; Mullis 2002), which is however biased against absorbed AGNs. Recently, Yang et al. (2003) performing a counts-in cells analysis of a deep ( f 2 - 8 k e " 3x erg s-l cme2) Chandru survey in the Lockman Hole North-West region, found that the hard band sources are highly clustered with 60% of them being distributed in overdense regions. In this study we use a hard (2-8 keV) X-ray selected sample, compiled from a shallow (2-10 ksec per pointing) XMM-Newton survey near the North and South Galactic Pole regions. A total of 18 pointings were observed out N
-
*Work partially supported by CONACyT grant 2002-cO1-39679
425
426
of which only 5 were discarded due to elevated particle background at the time of the observation. A full description of the data reduction, source detection and flux estimation are presented by Georgakakis et al. (2004). Here we just note that it comprises of 171 sources above the 50 detection ergs-' cm-2. threshold to the limiting flux of fx(2 - 8 keV) x
2. Correlation function analysis
In the present study we use as the estimator of the 2-point correlation function the following: w(0) = f (NDDINDR)- 1,where NOD and NDR is the number of data-data and data-random pairs respectively at separations 0 and 6 do. In the above relation f is the normalization factor f = ~ N R / ( ND1) where ND and NR are the total number of data and random points, respectively. To account for the different source selection and edge effects, we have produced 100 Monte Carlo random realizations of the source distribution within the area of the survey by taking into account variations in sensitivity which might affect the correlation function estimate. Indeed, the flux threshold for detection depends on the off-axis angle from the center of each of the XMM-Newton pointings. Since the random catalogues must have the same selection effects as the real catalogue, sensitivity maps are used to discard random points in less sensitive areas (close to the edge of the pointings). This is accomplished, to the first approximation, by assigning a flux to the random points using the Baldi et al. (2002) 2-10 keV log N-log S (after transforming to the 2-8keV band assuming = 1.7). If the flux of a random point is less than 5 times the local rms noise (assuming Poisson statistics for the background) the point is excluded from the random dataset. We note that the Baldi et al. (2002) log N - log S is in good agreement with the 2-8 keV number counts estimated in the present survey. The results of our analysis are shown in Figure 1, were the line corresponds to the best-fit power law model w(6') = (e,/e)~-' using the standard x2 minimization procedure in which each correlation point is weighted by its error. We find a statistically significant signal with w(t9 < 300") N 0.13 f 0.03 at the 4 . 3 ~ confidence level using Poissonian errors. The best +15.8 fit clustering parameters are: 0, = 48.9-,,,, and y = 2.2 f 0.30, where the errors correspond to la uncertainties. Fixing the correlation function slope to its nominal value, y = 1.8, we estimate eo = 22.22::; arcsec. Our results show that hard X-ray sources are strongly clustered, even more than the soft ones (see Vikhlinin & Forman 1995; Yang et al. 2003; Basilakos et al. in preparation). Our derived angular correlation length
+
427
10
1
0.01
0.001
100
1000
B(arcsec) Figure 1. The 2-point angular correlation function of the hard (2-8 keV) X-ray sources. Insert: 1 s o - A ~contours ~ in the y-Oo parameter space.
0, is in rough agreement, although somewhat smaller (within la) with the Chandra result of B0 = 40 f 11 arcsec (Yang et al. 2003). The stronger angular clustering with respect to the soft sources could be either due to the higher flux limit of the hard XMM-Newton sample, resulting in the selection of relatively nearby sources, or could imply an association of our hard X-ray sources with high-density peaks 3. The spa t i a l correlation length using w(0)
The angular correlation function w(0) can be obtained from the spatial one, < ( r ) ,through the Limber transformation (Peebles 1980). If the spatial z ) - - ( ~ +.~ The ) correlation function is modeled as 0.1 from the Chandra X-ray Observatory archive. We have developed an automated pipeline to reduce the data, detect sources and analyse the results. Our project will focus on the statistical excess of point sources in cluster fields compared to blank fields. Extensive calibration is being undertaken to determine the degree of field to field variation in non-cluster fields, and to identify any small systematic effects that could dominate over many fields. We will investigate the trends in the excess of point sources with cluster redshift, luminosity and morphology. In addition our automated pipeline analyses AGN luminosity and radial position within the cluster (as described for the two examples above) for all the clusters in the sample. With this major survey, we will determine how the properties of cluster AGN depend on redshift and environment. This will identify some of the mechanisms that trigger or suppress AGN activity.
References 1. 0. Johnson et al., MNRAS 243,924 (2003). 2. S.M. Molnar et al., A p J 573,L91 (2002). 3. P. Martini et al., A p J 576,L109 (2002).
LARGE-SCALE RADIO STRUCTURE IN THE UNIVERSE: GIANT RADIO GALAXIES
M. JAMROZY AND U. KLEIN Radioastronomisches Institut der Universitat Bonn, Auf dem Hugel 71, 0-53121 Bonn, Germany E-mail:
[email protected] J. MACHALSKI Obserwatorium Astronomiczne Uniwersytetu Jagelloriskiego, ul. Orla 171, Pl-30244 Krakdw, Poland K.-H. MACK Istituto d i Radioastronomia, Via P. Gobetti 101, 1-40129 Bologna, Italy Giant radio galaxies (GRGs), with linear sizes larger than 1 Mpc (Ho = 50 km s-l Mpc-’), represent the biggest single objects in the Universe. GRGs are rare among the entire population of radio galaxies (RGs) and their physical evolution is not well understood though for many years they have been of special interest for several reasons. The lobes of radio sources can compress cold gas clumps and trigger star or even dwarf galaxy formation, they can also transport gas from a host galaxy to large distances and seed the IGM with magnetic fields. Since GRGs have about 10 to 100 times larger sizes than normal RGs, their influence on the ambient medium is correspondingly wider and is pronounced on scales comparable to those of clusters of galaxies or larger. Therefore giants could play an important r d e in the process of large-scale structure formation in the Universe. Recently, thanks to the new all sky radio surveys, significant progress in searching for new GRGs has been made.
The main goal of our present research is to build a homogeneous database of all known GRGs and to use the information in a comprehensive study of various physical properties of the entire population. Our sample of GRGs comes from a compilation performed by Ishwara-Chandra & Saikia [l]as well as from three recent systematics searches for new giants [2, 3, 41. They are supplemented with a few additional sources taken from other papers. The list of the GRGs will be published later”. Some preliminary results from aThe list of GRGs can be obtained from: http://www.astro.uni-bonn.de/Nmjarnrozy
431
432 statistical studies of the properties of this GRG sample are the following: 0
0 0
0 0
0
The sample contains 125 sources, 106 of which have FRII-type structures, 8 are of FRI class and the remaining 11 have a hybrid FRII/FRI morphology. Only 11 giants of the entire sample are identified with quasars. Surprisingly, about 66% of the GRGs reported in [2] and [3] do not show any emission lines in their optical spectra and can be classified as low-excitation radio galaxies (LERGs). The bulk of GRGs are external of dense clusters. 7 GRGs are of a double-double type. Objects of this class show two pairs of lobes, presumably originating from an old and a new cycle of activity [5]. Only about 18% of the presently known GRGs have negative declinations, and the majority of them are nearby objects with high flux density. Therefore, one can expect a large number of yet undetected GRGs in the southern hemisphere. Table 1. Mean values of physical parameters of GRGs synchrotron age t entire volume V equipartition magnetic field Be, cocoon pressure pc jet power QO
total energy delivered by the twin jets Etot energy stored in the cocoon U,,
10" [yrl [m3]
0.3 [nT] [N m-2] 7 ~ 1 [J 0 s-l] ~ ~ 4x
[J]
3 ~ 1 [J] 0 ~ ~
Table 1 shows mean values of some physical parameters of GRGs which are derived from the observational data and the models of their dynamical evolution [6].
References 1. C.H. Ishwara-Chandra & D.J. Saikia, M N R A S 309,100 (1999). 2. L. Lara, W.D. Cotton, L. Feretti, G. Giovannini, 3. M. Marcaide, I. Marquez & T. Venturi, A&A 370,409 (2001). 3. J . Machalski, M. Jamrozy & S. Zola, A H A 371,445 (2001). 4. A. P. Schoenmakers, A. G. de Bruyn, H. J. A. Rottgering & H. van der Laan, A&A 374,861 (2001). 5. A. P. Schoenmakers, A. G. de Bruyn, H. J. A. Rottgering, H. van der Laan, H. & C. R. Kaiser, MNRAS 315,371 (2000). 6. J. Machalski, K. Chyiy & M. Jamrozy, astro-ph/0210546 (2004).
HIGH-REDSHIFT LYCX FOREST LINES IN A CONCORDANCE ACDM UNIVERSE
J. WAGG,l A. BABUL,' R. DAVE,3 S. ELLISON' AND A. SONGAILA4 Instituto Nacional de Astrofisica, Optica y Electrdnica (INAOE), Aptdo. Postal 51 y 216, Puebla, Mexico (
[email protected]) Department of Physics and Astronomy, University of Victoria, BC, Canada Astronomy Department, the University of Arizona, 933 North Cherry Avenue, Tucson, AZ, USA 85721 41FA, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI, USA 96822
It is generally accepted that the Lycr forest of QSO absorption lines arises due to absorption by HI in the intervening intergalactic medium (IGM). This gas traces the underlying dark-matter distribution and is believed to comprise most of the visible baryons in the Universe at redshifts z > 2. Within this theoretical framework, comparison of the observed spectra with predictions of cosmological hydro-simulations provides valuable insight into the environment and structure of the high-redshift Universe.
295 -
-11
h
4
-13
2.75
-
255
-
h
2 $
.
h
-3 v
-15
P , M 2 -17
235 -
215
-19
13
14
16
17
-
0.525
0.55
0.575 l o ~ ~ 1 6 1 + z ~ 6 2 50.65
0.675
Figure 1. Left: The column density distribution for HI absorption lines identified in both observed and simulated spectra. Right: The N H I dependence of line number density evolution calculated for simulations (filled diamonds) and observations (open squares).
Rather than study the fluctuating HI opacity in Lycr forest spectra (a
433
434
measure of physical over-density), we consider the statistics of individual HI absorption lines in the redshift range 2.5 < z < 3.7. The data include 5 QSO spectra (HIRES/KECK)3>5which are compared with 1000 simulated spectra extracted at various redshifts from a RCDM hydrodynamic simulation (SPH, 2 ~ 1 2 particles 8~ in a 22.2 h-lMpc box, R*=.7, Rm=.3 and h=.7). In order to reproduce the high fraction of ionized Hydrogen in the IGM, the simulation includes a UV background radiation field4. Line-lists are generated from both observed and simulated spectra using AutoVPl which fits the redshift, HI column density ( N H I )and doppler width of each line. Due t o differences in the resolution of the spectra and possible contamination of our sample by metal lines, we only include lines with doppler widths exceeding a physical lower-limit2. Although the results presented here are preliminary, the full details of our analysis and conclusions will be presented in an upcoming paper (Wagg et al., 2004 in prep.). Fig. 1 (left) shows the column density distribution of HI lines calculated for observed and simulated spectra. Both curves exhibit remarkable agreement over four decades in column density. The number density evolution of Lya forest lines is governed by i) the cosmological expansion, ii) the formation of structure and iii) the background intensity of ionizing radiation. We compare the redshift evolution of observed and simulated lines across four ranges in HI column density (right panel Fig. 1). The simulations appear to over-predict the number density of lines for redshifts z < 3.3, a difference which becomes more pronounced with increasing N H I . There have been recent suggestions that at redshifts, 3.0 < z < 3.5, He I1 was reionized. Reionization of He I1 increases the temperature of the IGM, thereby decreasing the neutral Hydrogen fraction and lowering the HI opacity of the Lya forest. A lower opacity a t these redshifts could explain the observed discrepancy in the number density evolution. Acknowledgments
J W is grateful for financial support through a scholarship from INAOE and support from CONACYT grant 39953-F. References
R. Dave, L. Hernquist, D.H. Weinberg & N. Katz, ApJ 477,21 (1997). R. Dave & T.M. Tripp, ApJ 553, 528 (2001). S.L. Ellison et al., PASP 111,946 (1999). F. Haardt Ek P. Madau, A p J 461,20 (1996). 5. E.M. Hu, T. Kim, L.L. Cowie, A. Songaila & M. Rauch, A J 110, 1526 (1995).
1. 2. 3. 4.
Author Index
Akiyama, M., 339 Akylas, A . , 25 Aldcroft, T.,21, 33 Alexander, D., 129 Allen, M.,295 Aller, M., 295 Aller, H., 295 Almaini, O., 421, 429 Anderson, K . S. J., 247, 295 Anderson, S. F., 247 Arshakian, T. G., 137,139 Athey, A., 413
Bressan, A., 101, 103, 379 Brinkmann, J., 247 Brookes, M., 343 Brotherton, M., 291 Brown, M., 93 Brunner, H., 355 Brusa, M., 81 Burenkov, A. N., 199 Caldwell, J. A. R., 63 Cameron, R. A., 33 Cappi, M., 41, 309 Carilli, c. L., 109, 115 Carrasco, L., 103, 123,199, 255 Carrera, F. J., 17 Cavallotti, F., 353 Ceballos, M. T., 17 Chatzichristou, E., 399 Chavez, M., 103 Chavushyan, V. H., 139, 199, 303 Chiaberge, M., 217 Chiappetti, L.,39 Chillingarian, I., 199 Collin, S., 199 Comastri, A., 43, 323 Conselice, C. J., 399 Cox, P., 109, 115 Crawford, C. S., 231 Croft, S., 133 Croom, S., 57,93 Cruz-GonzLlez, I., 195, 303 Cruz, M. J., 141 Czerny, B.,351
Babul, A., 433 Barbieri, C., 95 Barcons, X., 17 Barden, M., 63 Barkhouse, W., 21, 33 Barrio, F. E., 133 Basilakos, S., 25, 425 Bassani, L., 41, 309 Bauer, A., 133 Bauer, F., 5 Beckwith, S.V. W., 63 Beelen, A . , 109, 115 Bell, E. F., 63 Benitez, E., 201, 299, 303,397 Berta, S.,101 Bertoldi, F., 109, 115 Best, P. N., 343, 421, 429 Binette, L., 299 Blundell, K. M., 141 Borch, A., 63 Borisov, N., 199 Boyle, B., 57 Braatz, J., 227 Brand, K., 417 Brandt, W.N., 287
Dadina, M., 41, 309 Danese, L., 379 Daugherty, T., 295 D a d , R., 433
435
436 de Diego, J. A., 97, 397 Dey, A . , 93 De Zotti, G., 379 Di Cocco, G., 41 Doroshenko, V. T., 199 Dowsett, R., 429 Dultzin-Hacyan, D., 97, 195, 395 Dumont, A.-M., 199 Dunlop, J. S., 389 Duschl, W. J., 393 Dwelly, T., 35 Eckart, M. E., 37 Ellison, S., 433 Elvis, M., 275 Fabian, A . C., 231, 239, 355 Falcke, H., 169 Fioktistova, I. S., 199 Fiore, F., 11, 239 Fossati, G., 143 Franceschini, A,, 101 Francis, P. J., 105 Franco-Balderas, A., 195, 201, 395, 397 Freudling, W., 89 Fuentes-Carrera, I., 195 GaCeSa, M., 53 Gandhi, P., 231 Gelbord, J. M., 253, 305 Georgakakis, A , , 25, 425 Georgantopoulos, I., 25, 425 Ghinassi, F., 77 Ghosh, H., 33 Giannakis, O., 25 Gilli, R., 407 GonzBlez-Pkrez, J. N., 97 Goodlet, J. A., 145 Granato, G. L., 103, 335, 379 Greenhill, L. J., 227 Green, P. J., 21, 33 Green, R., 93, 291 Griffiths, R. E., 29 Grogin, A., 399 Guainazzi, M., 239, 307
Gunn, J. E., 53 Gunn, K. F., 147 Haas, M., 281 Hall, P. B., 47, 53, 93, 247 Haro-Corzo, S. A . R., 299 Harrison, F. A., 37 Hasinger, G., 355 Haussler, B., 63 Heckrnan, T. M., 187, 365 Helfand, D. J., 37 Henkel, C., 227 Hernandez-Martinez, L., 193 HernBndez-Toledo, H. M., 195, 395 Hidalgo, J. C., 243 Hill, G. J., 133, 417 Ho, L. C., 153 Hoyle, F., 57 Hutchings, J., 291 Ivezic, Z., 53 Iwasawa, K., 239, 309 Jagoda, A. S., 53 Jahnke, K., 63 Jamrozy, M., 431 Janiuk, A . , 351 Jannuzi, B., 33, 93 Jarvis, M. J., 133, 141 Jimknez, E., 307 Jimenez-Garate, M. A., 191 Jogee, S., 63 Johnson, O., 421, 429 Juarez, Y . , 77 JuriC, M., 53 Kaiser, C. R., 145 Kauffmann, T. M., 365 Kelson, D. D., 413 Kelson, D. D., 413 Khu, T., 191 Kim, D., 21, 33 Kitsionas, S., 25 Klein, U., 431 Knapp, G. R., 53, 247 Knudson, A., 29
437 Kolokotronis, V., 25 Koratkar, A . , 295 Kriss, G., 179, 291 Krolik, J. H., 295 Krongold, Y . 299 Kukula, M., 373 La Franca, F., 329 Laird, E. S., 37 Le FBvre, O., 39 Levenson, N. A., 187 Lister, M. L., 137 Loaring, N., 57, 73 Londish, D., 311 Lopes, A., 57 Lupton, R. H., 53 Maccagni, D., 39 Machalski, J., 431 Mack, K.-H, 431 Madejski, G., 295 Maiolino, It., 77, 235, 335 Majewski, P., 105 Mannucci, F., 77 Mao, P. H., 37 Maraschi, L., 39 March& M. M. J., 347 Marscher, A , , 295 Martinez, 0. M., 199 Martini, P., 413 Mateos, S., 17, 355 Matt, G., 239 Matute, I., 329 Mayya, D., 103, 193 M'Hardy, I., 147 McIntosh, D. H., 63 McLure, R., 389 Meisenheimer, K., 63 Memola, E., 275 Mendoza, S., 243 Menten, K. M., 115 Mercado, A , , 255 Mignoli, M., 257 Miller, L., 57, 73 Miyaji, T., 29, 317, 339
Moran, J. M., 227 Mossman, A., 33 Mujica, R., 77, 303 Mulchaey, J. S., 413 Murayama, T., 197 Myers, A,, 57 Nagm, T., 197 Nagar, N. M., 77, 169 Norman, D., 93 Ohta, K., 339 Oliva, E., 77 Omizzolo, A . , 95 Omont, A., 109, 115 Oshlack, A . , 105 Outram, P., 57 Padovani, P., 295 Page, M. J., 35 Paioro, L., 39 Panessa, F., 309 Pedani, M., 77 Peng, C. Y . , 63 Perlman, E., 295 Piconcelli, E., 41, 307 Pierre, M., 39 Plionis, M., 25, 425 Pozzetti, L., 257 Pursimo, T., 311 Ramirez, A,, 97 Ranalli, P., 43 Rawlings, S., 133, 141, 417 Recillas, E., 123 Rector, T., 295, 311, 353 Reichard, T. A., 47 Richards, G., 47, 53, 247 Rigopoulou, D., 101 Risaliti, G., 275 Rix, H.-W., 63 Rodighiero, G., 101 Rodriguez-GonzAlez, A . , 259 Rodriguez-Martinez, M., 299 Rodriguez-Pascual, P., 239 Rosado, M., 195
438 Ros, E., 137, 139 Rossi, C., 95 SBnchez-Fernbndez, C., 85 Sanchez, S. F., 63 sato, Y., 313 Schartel, N., 307 Schlegel, D., 53 Schloerb, F. P., 123 Schmitt, H., 183 Schneider, D.P., 47, 247, 287 Scott, J., 291 Setti, G.,43 Seymour, N., 147 Shanks, T., 25, 57 Shapovalova, A. I., 199 Shull, J. M., 291 Siemiginowska, A., 351 Silich, S.,259 Silva, L., 103, 335,379 Silverman, J., 21,33 Siverd, R. J., 53 Smith, M. G., 93 Smith, P. S., 93 Smith, R., 57 SmolEi6, V., 53 Snedden, S. A , , 247 Sobolewska, M., 351 Somerville, R. S., 63 Songaila, A., 433 Steed, A., 401 Steinhardt, W., 53 Stepanian, J. A., 303 Stern, D., 37 Stewart, G. C., 25 Stocke, J. T., 295, 353 Strauss, M. A., 47, 53, 247 Sturm, E., 163 Surdej, J., 39 Szczerba, R., 351 Tajer, M., 39 Taniguchi, Y., 197 Tenorio-Tagle, G., 259 Terlevich, E., 403
Terlevich, R., 403 Tiede, G., 93 Tornikoski, M., 311 Torrealba, J., 201 Torres-Papaqui, J. P.,403 Treister, E.,69, 99 Trinchieri, G., 39 Tufts, J., 417 Ueda, Y., 339 Urry, M., 69,99 Valdes, J. R., 101,199 Valibe, M.,25 Vanden Berk, D. E., 47, 247 Vega, O., 103 Veilleux, S., 205 Vestergaard, M.,385 Vignali, C., 287 Vlasuyk, V. V., 199 Wagg, J., 433 Wagner, S., 295 Walter, F., 115 Warren, S., 93 Weaver, K. A., 187, 253 Webster, R.L., 105 Weinberg, D. H., 401 Whiting, M. T., 105 Wiita. P.,53 Wilkes, B. J., 21, 33, 263 Wilson, A. S., 169, 227 Wisotzki, L., 63 Wolf, C.,63 Wolter, A., 353 Worsley, M.,231, 355 Yaqoob, T., 253 York, D. G., 247 Yost, S. A., 37 Yu, Q., 359 Zappacosta, L., 235 Zensus, J. A., 137, 139 Zheng, W., 291
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