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The Formation and Growth of the First Black Holes A Whitepaper for the 2010 Decadal Survey Science Frontier Panel Galaxies across Cosmic Time GCT Authors Bret Lehmer Durham University Niel Brandt Penn State University Dave Alexander Durham University Roger Brissenden Smithsonian Astrophysical Obsevatory Martin Elvis Smithsonian Astrophysical Obsevatory Ann Hornschemeier Goddard Space Flight Center Dan Schwartz Smithsonian Astrophysical Obsevatory the Generation X Team Contact Person Bret Lehmer Department of Physics Durham University South Road Durham DH1 3LE UK Email b d lehmer dur ac uk Telephone 44 191 334 3773 1 1 Introduction The path of observational cosmology over the next decade will be focused on the exploration of the early Universe To determine how the phenomena i e galaxies stars planets etc of our local Universe evolved to their present state we must determine how and when the first stars galaxies and black holes formed In the next decade observatories such as JWST ALMA LSST TMT GMT and E ELT will provide a phenomenal new perspective on this theme allowing for the first time in history a direct view of the starlight that originates from the first galaxies a regime that is only now understood by theoretical inferences However it is now clear that galaxy and black hole growth are intimately tied and therefore knowledge of black hole formation and growth is required to piece together a complete picture of galaxy formation Specifically we will need observational facilities designed to address the following questions How and when did the first black holes in the Universe form and grow What influence did the energetic process of accretion onto the first black holes have on the formation and evolution of their host galaxies and in reionizing the Universe Addressing these questions requires sensitive X ray observations which effectively probe the nearby vicinity of the accreting black holes even through heavily obscured environments The next great X ray observatory the International X ray Observatory IXO will provide the first key discoveries of luminous accreting supermassive black holes SMBHs out to z 7 8 and constrain the physical processes responsible for powering these sources To extend the findings from IXO and study for the first time the evolution of representative populations of seed black holes from their birth around z 8 15 requires an X ray observatory capable of detecting extremely faint sources with 0 1 10 keV fluxes of 10 20 ergs cm 2 s 1 while remaining free from source confusion To achieve these aims requires an observatory with an effective light collecting area of 50 100 m2 and a resolution of 0 1 these specifications can provide imaging that is 1000 times deeper and 5 times higher resolution than Chandra The Generation X mission specifications have been designed with these requirements in mind Here we illustrate how Generation X will optimally address these questions 2 The First Black Holes How and when did the first black holes in the Universe form Theoretical studies of star formation in the early Universe require that the first populations of black 260 M ending their short holes were formed at z 15 20 as a result of the first massive stars lives e g Bromm et al 1999 Gao et al 2007 The initial masses of such black holes will be more than half that of the progenitor star e g Heger Woosley 2002 and it is expected that these stars will produce a population of black holes with masses of order 100 M Though the details are not yet clear these black holes are expected to lie in nebulous overdense halos and so shortly after their formation they will merge with neighboring halos to form increasingly more massive overdensities Through this process the black holes can grow both via mass accretion and black hole black hole mergers Volonteri et al 2003 As the gas in these overdense regions cools new generations of stars will form and these first galaxies and black holes will continue to grow 2 through accretion X ray observations provide a very effective means for probing the conditions in the immediate vicinity of accreting black holes and are capable of penetrating through thick columns of obscuring material We now know from deep Chandra and XMM Newton data that the X ray band is at present the most effective way of identifying and studying large populations of accreting supermassive black holes SMBHs seen as active galactic nuclei AGNs over a wide range of luminosities and over the entire history of the Universe e g Brandt Hasinger 2005 The deepest X ray surveys conducted with Chandra Alexander et al 2003 Luo et al 2008 find about ten times more AGNs per square degree than the deepest optical surveys e g Bauer et al 2004 and many of which cannot be identified via optical spectroscopy e g Barger et al 2005 Beyond the local universe the best way to find SMBHs will be to search for nuclear activity probed by X ray emission The X ray signatures of an accreting black hole are very clear even out to z 6 a luminous X ray source with a hard powerlaw spectrum extending to high energies e g Shemmer et al 2006 At even higher redshifts the 0 1 10 keV bandpass probes hard rest frame X ray energies which are capable of penetrating extremely thick obscuring environments reaching optical extinctions of 100s to 1000s of magnitudes It is known from observational studies of local galaxies and their nuclear environments that by the present day nearly all nucleated galaxies host SMBHs in their centers e g Kormendy Richstone 1995 Magorrian et al 1998 It has also been recently discovered that the masses of these SMBHs are strongly correlated with the masses of the giant stellar bulges residing in the host galaxies e g Gebhardt et al 2000 A key inference from these observations is that SMBHs and their host galaxies grew in tandem with the growth of each component influencing that of the other despite the host galaxy being 109 times larger in physical size and 1000 times more massive than the SMBH Therefore a more complete understanding of how galaxies and their SMBHs formed and evolved together requires observations constraining the formation of both the first black holes and galaxies While there are several paths to the formation of SMBHs e g Rees 1984 the fact that the SMBH galaxy bulge mass relationship holds in the local Universe constrains models Some of the black holes may have grown via Eddington accretion from a seed black hole while others may have formed through the direct


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