Civano, F. and Brusa, M. and Comastri, A. and Elvis, M. and Salvato, M. and Zamorani, G. and Capak, P. and Fiore, F. and Gilli, R. and Hao, H. and Ikeda, H. and Kakazu, Y. and Kartaltepe, J. S. and Masters, D. and Miyaji, T. and Mignoli, M. and Puccetti, S. and Shankar, F. and Silverman, J. and Vignali, C. and Zezas, A. and Koekemoer, A. M. (2011) The Population of High-Redshift Active Galactic Nuclei in the CHANDRA-Cosmos Survey. Astrophysical Journal, 741 (2). Art. No. 91. ISSN 0004-637X. http://resolver.caltech.edu/CaltechAUTHORS:20120123-115613901
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We present the high-redshift (3 <z < 5.3) 0.5-2 keV number counts and the 2-10 keV (rest-frame) space density of X-ray-selected active galactic nuclei (AGNs) detected in the Chandra Cosmic Evolution Survey. The sample comprises 81 X-ray-detected sources with available spectroscopic (31) and photometric (50) redshifts plus 20 sources with a formal z_(phot) < 3 but with a broad photometric redshift probability distribution, such that z_(phot) + 1σ > 3. Eighty-one sources are selected in the 0.5-2 keV band, fourteen are selected in the 2-10 keV and six in the 0.5-10 keV bands. We sample the high-luminosity (log L_((2-10keV)) > 44.15 erg s^(–1)) space density up to z ~ 5 and a fainter luminosity range (43.5 erg s^(–1) < log L_((2-10keV)) < 44.15 erg s^(–1)) than previous studies, up to z = 3.5. We weighted the contribution to the number counts and the space density of the sources with photometric redshift by using their probability of being at z > 3. We find that the space density of high-luminosity AGNs declines exponentially at all the redshifts, confirming the trend observed for optically selected quasars. At lower luminosity, the measured space density is not conclusive, and a larger sample of faint sources is needed. Comparisons with optical luminosity functions and black hole formation models are presented together with prospects for future surveys.
|Additional Information:||© 2011 The American Astronomical Society. Received 2010 December 23; accepted 2011 August 8; published 2011 October 21. The authors thank the referee for suggestions which improved this paper’s content. The authors thank J. Aird and E. Glikman for sharing their luminosity functions, and G. Risaliti, R. D’Abrusco, and A. Goulding for useful discussions. This work was supported in part by NASA Chandra grant No. GO7-8136A (M.E., F.C., H.H.), the Blancheflor Boncompagni Ludovisi foundation (F.C.) and the Smithsonian Scholarly Studies (F.C.). F.S. acknowledges the Alexander von Humboldt Foundation for support. In Italy this work is supported by ASI/INAF contracts I/009/10/0 and I/088/06. Facilities: CXO (ACIS), HST (ACS), XMM|
|Subject Keywords:||evolution; galaxies: active; surveys; X-rays: galaxies|
|Official Citation:||The Population of High-redshift Active Galactic Nuclei in the Chandra-COSMOS Survey F. Civano et al. 2011 ApJ 741 91|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||24 Jan 2012 16:10|
|Last Modified:||06 Jul 2015 20:00|
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