SUPERMASSIVE BLACK HOLES IN THE DISTANT UNIVERSE ASTROPHYSICS AND SPACE SCIENCE LIBRARY VOLUME 308 EDITORIAL BOARD Chairman W.B. BURTON, National Radio Astronomy Observatory, Charlottesville, Virginia, U.S.A. ([email protected]); University of Leiden, The Netherlands ([email protected]) Executive Committee 1. M. E. KUIIPERS, Faculty of Science, Nijmegen, The Netherlands E. P. 1. VAN DEN HEUVEL, Astronomical Institute, University of Amsterdam, The Netherlands H. VAN DER LAAN, Astronomical Institute, University of Utrecht, The Netherlands MEMBERS I. APPENZELLER, Landessternwarte Heidelberg-Konigstuhl, Germany 1. N. BAHCALL, The Institute for Advanced Study, Princeton, US.A. F. BERTOLA, Universitd di Padova, Italy 1. P. CASSINELLI, University of Wisconsin, Madison, US.A. C. 1. CESARSKY, Centre d'Etudes de Saclay, Gif-sur-Yvette Cedex, France O. ENGVOLD, Institute of Theoretical Astrophysics, University of Oslo, Norway R. McCRAY, University of Colorado, JILA, Boulder, US.A. P. G. MURDIN, Institute ofA stronomy, Cambridge, UK. F. PACINI, Istituto Astronomia Arcetri, Firenze, Italy V. RADHAKRISHNAN, Raman Research Institute, Bangalore, India K. SATO, School of Science, The University of Tokyo, Japan F. H. SHU, University of California, Berkeley, US.A. B. V. SOMOV, Astronomical Institute, Moscow State University, Russia R. A. SUNYAEV, Space Research Institute, Moscow, Russia Y. TANAKA, Institute of Space & Astronautical Science, Kanagawa, Japan S. TREMAINE, CITA, Princeton University, U.S.A. N. O. WEISS, University of Cambridge, UK. SUPERMASSIVE BLACK HOLES IN THE DISTANT UNIVERSE Edited by AMY 1. BARGER Department ofA stronomy, University of Wisconsin-Madison, U.S.A.; and Department of Physics and Astronomy, University of Hawaii, Honolulu, U.S.A.; and Institute for Astronomy, University of Hawaii, Honolulu, U.S.A. SPRINGER-SCIENCE+BUSINESS MEDIA, B.Y. A c.I.P. Catalogue record for this book is available from the Library of Congress. ISBN 978-90-481-6662-6 ISBN 978-1-4020-2471-9 (eBook) DOI 10.1007/978-1-4020-2471-9 Cover picture: The deepest X-ray observation of the universe: a Chandra X-ray image of the Hubble Deep Field-North region and its environs. Image courtesy of NASAIPSU/ D.M. Alexander, F.E. Bauer, W.N. Brandt, G.P. Garmire, et al. See Alexander et al. (2003, AJ, 126,539) for details. Printed on acid-free paper All Rights Reserved © 2004 Springer Science+Business Media Dordrecht Originally published by Kluwer Academic Publishers in 2004 Softcover reprint of the hardcover 1s t edition 2004 No part of this work may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission from the Publisher, with the exception of any material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. TABLE OF CONTENTS Preface vii Chapter 1 Observational Evidence for Supennassive Black Holes 1 L. Ferrarese Chapter 2 How are AGN Found? 53 R. Mushotzky Chapter 3 Theory of Disk Accretion onto Supennassive Black Holes 89 P.J Armitage Chapter 4 Modeling the Accretion History of Supennassive Black Holes 127 P. Natarajan Chapter 5 The Fonnation and Evolution of the First Massive Black Holes 147 Z. Haiman and E. Quataert Chapter 6 A Panchromatic View of AGN 187 G. Risaliti and M Elvis Chapter 7 Distant X-Ray Galaxies: Insights from the Local Population 225 E.C. Moran v VI Table of Contents Chapter 8 Compton-Thick AGN: The Dark Side ofthe X-Ray Background 245 A. Comastri Chapter 9 The Accretion History of Supermassive Black Holes 273 L.L. Cowie and A.J. Barger Preface Quasars, and the menagerie of other galaxies with "unusual nuclei", now collectively known as Active Galactic Nuclei or AGN, have, in one form or another, sparked the interest of astronomers for over 60 years. The only known mechanism that can explain the staggering amounts of energy emitted by the innermost regions of these systems is gravitational energy release by matter falling towards a supermassive black hole --- a black hole whose mass is millions to billions of times the mass of our Sun. AGN emit radiation at all wavelengths. X-rays originating at a distance of a few times the event horizon of the black hole are the emissions closest to the black hole that we can detect; thus, X-rays directly reveal the presence of active supermassive black holes. Oftentimes, however, the supermassive black holes that lie at the centers of AGN are cocooned in gas and dust that absorb the emitted low energy X-rays and the optical and ultraviolet light, hiding the black hole from view at these wavelengths. Until recently, this low-energy absorption presented a major obstacle in observational efforts to map the accretion history of the universe. In 1999 and 2000, the launches of the Chandra and XMM-Newton X-ray Observatories finally broke the impasse. The impact of these observatories on X-ray astronomy is similar to the impact that the Hubble Space Telescope had on optical astronomy. The astounding new data from these observatories have enabled astronomers to make enormous advances in their understanding of when accretion occurs. In light of these exciting recent developments, it seemed like the ideal time to put together a book that would (a) assess where we currently stand, theoretically and observationally, in our understanding of the accretion history of supermassive black holes in the universe, and (b) mark the path we should take to answer any remaining open questions. There was also a hope that, by tying together contributions from both theorists and observers, clear mutual future directions for the field would become apparent. I believe that both of these goals have been met in this tremendously informative and thought provoking book. The book starts with an observational Chapter 1 by Laura Ferrarese on the current status of supermassive black hole research in the nearby universe. From these observations, we now not only have proof that supermassive black holes do indeed exist, but we also have discovered fundamental empirical relationships between the mass of the central black hole and the global Vll Vlll Preface properties of its host galaxy. These connections lead us to the realization that the assembly of a black hole and the formation of the stars in its host galaxy are intimately linked. Since the nearby, dormant supermassive black holes are the fossils of the active supermassive black holes of the distant past, we have a natural transition to Chapter 2 by Richard Mushotzky, who addresses how we actually find the active supermassive black holes at high redshifts. This is a tricky issue; different wavebands provide different windows onto our universe, so observations in only one waveband are likely to provide a skewed view of what all is out there. In the past, we have not had much choice -- ultraviolet or optical light was pretty much all we had available to us. Now, however, we have a smorgasbord of wavelengths to observe at, and Mushotzky discusses how some of these wavelengths are significantly less biased than others for finding those elusive supermassive black holes. When I say "elusive", I mean those black holes that are either obscured by gas and dust and hence not easily (or at all!) visible at ultraviolet and optical wavelengths, or those black holes that, for one reason or another, simply emit more light at wavelengths other than the ultraviolet or optical. The timescales and luminosities of the active supermassive black holes are determined both by the feeding of matter onto the black holes and by the physics of the accretion process. Thus, we segue into the Chapter 3 by Philip Armitage, who discusses our current theoretical understanding of black hole accretion. Armitage provides important insights into the viscous processes that govern the funneling of material through the accretion disk onto the supermassive black hole, and on the efficiencies with which the accreting material will radiate in various accretion regimes. These are both key elements in connecting the population of distant, active supermassive black holes to the nearby, dormant population. Now that we have a theoretical basis for the accretion process, we want to know how well theorists can do at modeling the accretion history of supermassive black holes. Chapter 4 by Priyamvada Natarajan discusses accretion history reconstruction using observations at high and low redshifts as model constraints. Two paths in theoretical modeling have so far been taken, a phenomenological approach that uses observations as constraints, and a semi-analytic approach that starts with a theoretical framework and a set of assumptions and aims to match the observations. There are some key issues and uncertainties in both approaches, with one major issue being the role of obscured sources. The book will come back to this important topic again later. It is certainly physically insightful to be able to construct models that match the current observations, but we would also like to see some models that give Preface IX predictions at epochs where our current observations cannot probe. In particular, we would like to know when the first massive black holes began to form and whether they played a role in the reionization of the intergalactic gas. Zoltan Haiman and Eliot Quataert look at this subject in Chapter 5, where the question they address is, how did the first massive black holes form? Haiman and Quataert describe the theoretical expectations for the formation and growth of the earliest black holes within the hierarchical cold dark matter cosmologies, summarize recent observations that have some bearing on this issue, and look to the future for observations that may be able to shed some light on the physics of the first massive black holes. With these theoretical frameworks in hand, we now return to the observations. In Chapter 2, Mushotzky described how to find distant, active supermassive black holes, but also how selection effects can skew our samples. We could really do with some additional knowledge on this topic, however; in particular, it would be very useful to know the nature of the spectral energy distributions of both unobscured and obscured sources in order to be able to determine the bolometric corrections that translate luminosities in a particular waveband to total luminosities. Chapter 6 by Guido Risaliti and Martin Elvis explores these issues using broad wavelength coverage from the X-rays to the infrared to the radio. Risaliti and Elvis also discuss ways to disentangle emission due to accretion from emission due to stars, which is a concern when using infrared light to determine bolometric corrections. Chandra and XMM-Newton have made great progress in resolving the hard (2-8 keY) X-ray background, whose origin has been one of the major mysteries of X-ray astronomy for almost 40 years. However, the optical follow-up of these sources has introduced some interesting new puzzles, including ones on the exact nature and evolution of the obscured sources. Our next chapter, Chapter 7 by Edward Moran, uses more local, active supermassive black holes, which are well characterized due to their proximity, to gain insights into the nature of the distant X-ray galaxies observed by Chandra and XMM-Newton, which are generally too faint to be studied in much detail. One important point that Moran makes is that there is a great need to be careful in making direct comparisons between the distant and more local populations because of the complicating effects of selection and data quality. Since the issue of obscuration is such a crucial one, our next chapter, Chapter 8 by Andrea Comastri, is entirely devoted to the contributions to the X-ray background from "Compton-thick" sources, whose absorbing matter has a significant optical depth for Compton scattering. Compton-thick sources appear to be very common in the nearby universe, but, unfortunately, we do not know how common they are in the distant universe, since even the most sensitive Chandra and XMM-Newton X-ray surveys are inefficient at