Toward the Standard Population Synthesis Model of the X-Ray Background: Evolution of X-Ray Luminosity and Absorption Functions of Active Galactic Nuclei Including Compton-Thick Populations

Abstract

We present the most up-to-date X-ray luminosity function (XLF) and absorption function of Active Galactic Nuclei (AGNs) over the redshift range from 0 to 5, utilizing the largest, highly complete sample ever available obtained from surveys performed with Swift/BAT, MAXI, ASCA, XMM-Newton, Chandra, and ROSAT. The combined sample, including that of the Subaru/XMM-Newton Deep Survey, consists of 4039 detections in the soft (0.5-2 keV) and/or hard (> 2 keV) band. We utilize a maximum likelihood method to reproduce the countrate versus redshift distribution for each survey, by taking into account the evolution of the absorbed fraction, the contribution from Compton-thick (CTK) AGNs, and broad band spectra of AGNs including reflection components from tori based on the luminosity and redshift dependent unified scheme. We find that the shape of the XLF at z ∼ 1 − 3 is significantly different from that in the local universe, for which the luminosity dependent density evolution model gives much better description than the luminosity and density evolution model. These results establish the standard population synthesis model of the X-Ray Background (XRB), which well reproduces the source counts, the observed fractions of CTK AGNs, and the spectrum of the hard XRB. The number ratio of CTK AGNs to the absorbed Compton-thin (CTN) AGNs is constrained to be ≈0.5-1.6 to produce the 20-50 keV XRB intensity within present uncertainties, by assuming that they follow the same evolution as CTN AGNs. The growth history of supermassive black holes is discussed based on the new AGN bolometric luminosity function.

The NuSTAR Extragalactic Surveys: X-Ray Spectroscopic Analysis of the Bright Hard-band Selected Sample

“…Given that 80% of the sources are at z 1  and that 90% of the contribution to the high-luminosity bin comes from sources at z 0.3 1.1 » -, we can compare our results with recent determinations at similar redshifts. We find broad consistency with the estimated fractions for Compton-thin sources reported by Ueda et al (2014) and Buchner et al (2015) for z 0.1 1 = -and z 0.5 0.75 = -, respectively. To give an idea of the variance of our results on the adopted binning, we adjusted the bin width in order to include up to eight more sources (thus increasing the number of sources by ∼25%) and reported the range of the corresponding variations as gray regions.…”

“…Indeed, several authors report a decrease in the absorbed AGN population with source luminosity (e.g., Lawrence & Elvis 1982;Steffen et al 2003;La Franca et al 2005;Sazonov et al 2007;Della Ceca et al 2008;Burlon et al 2011) and an increase with redshift at fixed X-ray luminosity (e.g., La Franca et al 2005;Ballantyne et al 2006;Treister & Urry 2006;Ueda et al 2014;Vito et al 2014). Our spectral analysis effectively probes rest-frame 1.2 24 keṼ -for all the sources, given the redshift distribution from z 0  up to z 1.5 » .…”

“…Indeed, they generally implement relatively similar assumptions. The reflection is always assumed to have a constant value R 1 » within each population (e.g., Ballantyne et al 2006;Treister et al 2009;Akylas et al 2012;Ueda et al 2014) or possibly a function of the degree of obscuration (e.g., G07; Ueda et al 2014;Esposito & Walter 2016) with no dispersion around a mean value. On average, we find median reflection values that are: (1) significantly lower (R 0.3 0.7 » -) than those assumed (R 1 » ) by CXB models and (2) exhibit a rather broad distribution with a median value relative to the whole sample of ∼0.4 (Table 6).…”

“…A population of AGN with column densities in excess of 10 24 cm 2 -, called Compton-thick (CT) AGNs, and numerically comparable to the absorbed Compton-thin AGN, has long been posited to be responsible for the unaccounted 10-25% of the CXB flux required by population-synthesis models in order to reproduce its peak at 20-30keV (Comastri et al 1995;Gilli et al 2007, hereafter G07). Recent works, however, suggest that the less obscured sources may also contribute significantly to the missing flux at 10 keV > once other relevant high-energy spectral complexities of the AGN spectrum are taken into proper consideration (Treister et al 2009;Akylas et al 2012;Ueda et al 2014). The latter would therefore lessen the need for a sizable contributing population of CT sources.…”

AGN Reverberation Mapping

“…The lifetime of a typical AGN event for a typical black hole is small compared to the age of the Universe, and is generally thought to be on the order of ∼ 10 8 years (e.g., Kelly et al 2010). Cosmic downsizing is observed in AGNs as it is in galaxies: the bright quasars we see in the early Universe are associated with massive black holes and large accretion rates, while today's active black holes tend to be fewer in number, less massive, and have smaller accretion rates (e.g., Ueda et al 2003Ueda et al , 2014Shankar et al 2009;Kelly et al 2010;Kalfountzou et al 2014).…”