Accretion properties of X-ray AGN: Evidence for radiation-regulated obscuration with redshift-dependent host galaxy contribution

We adopt a Bayesian X-ray spectral approach to investigate the accretion properties of unobscured (20 < log ( N H / cm −2 < 22) and obscured (22 < log ( N H / cm −2 < 24) active galactic nuclei (AGNs) to shed light on the orientation versus evolution scenarios for the origin of the obscuring material. For a sample of 3882 X-ray-selected AGN from the Chandra COSMOS Legacy, AEGIS, and CDFS extragalactic surveys, we constrain their stellar masses, M  , intrinsic X-ray luminosities, L X , obscuring column densities, N H , and specific accretion rates λ∝ L X /M  . By combining these observables within a Bayesian non-parametric approach, we infer, for the first time, the specific accretion rate distribution (SARD) of obscured and unobscured AGN to z ≈3, i.e. the probability of a galaxy with mass M  at redshift z hosting an AGN with column density N H and specific accretion rate λ. Our findings indicate that (1) both obscured and unobscured SARDs share similar shapes, shifting towards higher accretion rates with redshift, (2) unobscured SARDs exhibit a systematic offset towards higher λcompared to obscured SARD for all redshift intervals, (3) the obscured AGN fraction declines sharply at log λbreak ∼−2 for z < 0 . 5, but shifts to higher λvalues with increasing redshift, (4) the incidence of AGN within the theoretically unstable blow-out region of the λ−N H plane increases with redshift. These observations provide compelling evidence for AGN ‘downsizing’ and radiation-regulated nuclear-scale obscuration with an increasing host galaxy contribution towards higher redshifts.