The evolution of the X-ray luminosity functions of unabsorbed and absorbed AGNs out to z∼ 5

Abstract

We present new measurements of the evolution of the X-ray luminosity functions (XLFs) of unabsorbed and absorbed Active Galactic Nuclei (AGNs) out to z ∼ 5. We construct samples containing 2957 sources detected at hard (2-7 keV) X-ray energies and 4351 sources detected at soft (0.5-2 keV) energies from a compilation of Chandra surveys supplemented by wide-area surveys from ASCA and ROSAT. We consider the hard and soft X-ray samples separately and find that the XLF based on either (initially neglecting absorption effects) is best described by a new flexible model parametrization where the break luminosity, normalization and faint-end slope all evolve with redshift. We then incorporate absorption effects, separately modelling the evolution of the XLFs of unabsorbed (20 < log N H < 22) and absorbed (22 < log N H < 24) AGNs, seeking a model that can reconcile both the hard-and soft-band samples. We find that the absorbed AGN XLF has a lower break luminosity, a higher normalization, and a steeper faint-end slope than the unabsorbed AGN XLF out to z ∼ 2. Hence, absorbed AGNs dominate at low luminosities, with the absorbed fraction falling rapidly as luminosity increases. Both XLFs undergo strong luminosity evolution which shifts the transition in the absorbed fraction to higher luminosities at higher redshifts. The evolution in the shape of the total XLF is primarily driven by the changing mix of unabsorbed and absorbed populations.

Supermassive black holes in the EAGLE Universe. Revealing the observables of their growth

“…We show two simulations, Ref-L100N1504 (dark blue lines) and AGNdT9-L050N0752 (light blue lines). The HXRLF shows strong Green circles correspond to the observational estimates from Miyaji et al (2015), red pentagons to Aird et al (2015) and bright blue hexagons to Buchner et al (2015). Comparing the simulations to each other, we find good agreement at all redshifts with differences no larger than 0.2 dex in normalization.…”

“…Ueda et al 2003;Steffen et al 2003) Ueda et al 2014). Because of these uncertainties, we prefer to compare the simulations to observed soft X-ray luminosity functions for which the obscured fraction has already been taken into account by simultaneously fitting to both hard and soft Xray data (Aird et al 2015). In future work, we will investigate the obscuration of AGN due to gas and dust, taking into account the properties of the host galaxy.…”

“…This makes hard X-rays the least biased wavelength range to detect the full SMBH population as obscuration is greatly reduced. Recently, multiple large X-ray surveys have been carried out by Ueda et al (2014), SMBHs in EAGLE Universe 191 Aird et al (2015) and Buchner et al (2015). These studies have revealed that the AGN population evolves strongly and that their number density abruptly decreases between z ≈ (1-2) and today.…”

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

“…-) AGN population and further shed light on the known decreasing trend between the numerical relevance of this population compared to all AGN (absorbed fraction) and the source luminosity (Lawrence & Elvis 1982;Gilli et al 2007;Burlon et al 2011;Buchner et al 2015) and its redshift evolution (La Franca et al 2005;Ballantyne et al 2006;Treister & Urry 2006;Aird et al 2015a;Buchner et al 2015;Liu et al 2017). They also allow exploration of the importance of the CT population, although with different constraining power and different non-negligible degrees of bias-especially at the highest column densities and lowest luminosities (e.g., Burlon et al 2011;Brightman et al 2014;Buchner et al 2015;Lanzuisi et al 2015;Ricci et al 2015).…”

“…Model predictions from G07, U14, and Aird et al (2015a) are shown in dotted-dashed green, long-dashed orange, and short-dashed blue, respectively. 42 The fraction of the CT sources (relative to all AGN population) obtained with the best-fit slopes is rather high and uncertain, given its large uncertainties; see Table 8.…”