2011/03/31 by F. Civano, M. Brusa, A. Comastri +27 · 1 citation
Physics and Astronomy · #Active galactic nucleus #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Cosmic Phenomena #Galaxies: Formation, Evolution, Phenomena #Galaxy #Luminosity #Luminosity function #Physics #Population #Quasar #Redshift #astro-ph.CO #astro-ph.HE
paper · pdf · doi:10.1088/0004-637x/741/2/91
10 pages, 6 figures. ApJ in press. Table 3 is available in the published version
arxiv created 2011/09/01 · openalex publication_date 2011/10/21 · arxiv updated 2015/05/27 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
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.