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< (N ₇/ cm^-2<22) and obscured (22< (N ₇/ cm^-2<24) active galactic nuclei (AGN) to shed light on the orientation vs 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 ₗ, obscuring column densities, N ₇, and specific accretion rates L ₗ/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 z3, i. e. the probability of a galaxy with mass M_ at redshift z hosting an AGN with column density N ₇ and specific accretion rate. 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 compared to obscured SARD for all redshift intervals, (3) the obscured AGN fraction declines sharply at ₁ₑ₄₀₊ -2 for z <0. 5, but shifts to higher values with increasing redshift, (4) the incidence of AGN within the theoretically unstable blow-out region of the -N ₇ 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.