2003/08/31 by Yoshihiro Ueda, Masayuki Akiyama, Kouji Ohta +1 · 1 citation
Physics and Astronomy · #astro-ph
paper · pdf · doi:10.1086/378940
published as Astrophys.J.598:886-908,2003 · 62 pages, 26 figures (13 colour figures included). Accepted for publication in ApJ. Minor corrections. References are updated
arxiv created 2003/09/29 · arxiv updated 2009/12/01
We investigate the cosmological evolution of the hard X-ray luminosity function (HXLF) of Active Galactic Nuclei (AGN) in the 2-10 keV luminosity range of 1041.5 - 1046.5 erg s-1 as a function of redshift up to 3. From a combination of surveys conducted at photon energies above 2 keV with HEAO1, ASCA, and Chandra, we construct a highly complete (>96%) sample consisting of 247 AGNs over the wide flux range of 10-10 - 3.8*10-15 erg cm-2 s-1 (2-10 keV). For our purpose, we develop an extensive method of calculating the intrinsic (before-absorption) HXLF and the absorption (NH) function. This utilizes the maximum likelihood method fully correcting for observational biases with consideration of the X-ray spectrum of each source. We find that (i) the fraction of X-ray absorbed AGNs decreases with the intrinsic luminosity and (ii) the evolution of the HXLF of all AGNs (including both type-I and type-II AGNs) is best described with a luminosity dependent density evolution (LDDE) where the cutoff redshift increases with the luminosity. Our results directly constrain the evolution of AGNs that produce a major part of the hard X-ray background, thus solving its origin quantitatively. A combination of the HXLF and the NH function enables us to construct a purely "observation based" population synthesis model. We present basic consequences of this model, and discuss the contribution of Compton-thick AGNs to the rest of the hard X-ray background.