The Population of High-redshift Active Galactic Nuclei in the Chandra-COSMOS Survey

November 2011 • 2011ApJ...741...91C

Authors • Civano, F. • Brusa, M. • Comastri, A. • Elvis, M. • Salvato, M. • Zamorani, G. • Capak, P. • Fiore, F. • Gilli, R. • Hao, H. • Ikeda, H. • Kakazu, Y. • Kartaltepe, J. S. • Masters, D. • Miyaji, T. • Mignoli, M. • Puccetti, S. • Shankar, F. • Silverman, J. • Vignali, C. • Zezas, A. • Koekemoer, A. M.

Abstract • 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 _{(2-10 keV)} > 44.15 erg s^-1) space density up to z ~ 5 and a fainter luminosity range (43.5 erg s^-1 < log L _{(2-10 keV)} < 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.

Links

• PREPRINT http://arxiv.org/abs/1103.2570
• NED https://ned.ipac.caltech.edu/uri/NED::InRefcode/2011ApJ...741...91C
• ELECTR https://doi.org/10.1088%2F0004-637X%2F741%2F2%2F91
• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2011ApJ...741...91C
• PDF https://iopscience.iop.org/article/10.1088/0004-637X/741/2/91/pdf
• PDF https://stacks.iop.org/0004-637X/741/91/pdf
• DATA https://cda.harvard.edu/chaser?obsid=7995,7996,7997,7998,7999,8000,8001,8002,8003,8004,8005,8006,8007,8008,8009,8010,8011,8012,8013,8014,8015,8016,8017,8018,8019,8020,8021,8022,8023,8024,8025,8026,8027,8122,8123,8124,8478,8482,8483,8493,8494,8496,8497,8503,8549,8550,8552,8553,8555