Speaker
Description
Accreting supermassive black holes, or active galactic nuclei (AGN), are known to grow behind clouds of gas and dust, obscuring their view.
In orientation unification models, unobscured ($20<\log(N_{\rm H}/{\rm cm}^{-2}<22$) and obscured ($22< \log(N_{\rm H}/{\rm cm}^{-2}<24$) AGN differ only by their viewing angle, while evolutionary models suggest that obscuration correspond to a specific phase in the AGN life-cycle. Consequently, the former predicts similar accretion properties while the latter expect discernible differences.
To investigate this dichotomy, I analysed 3882 X-ray-selected AGN from three different {\it Chandra} deep extragalactic fields (COSMOS Legacy, CDFS, AEGIS) and constrained their stellar masses, $M_\star$, intrinsic X-ray luminosities, $L_{\rm X}$, obscuring column densities, $N_{\rm H}$, and specific accretion rates $\lambda\propto L_{\rm X}/M_\star$.
By combining these observables within a Bayesian non-parametric approach, I infered, for the first time, the specific accretion rate distribution (SARD) of obscured and unobscured AGN to $z\approx3$, i.e. the probability of a galaxy with mass $M_\star$ at redshift $z$ hosting an AGN with column density $N_{\rm H}$ and specific accretion rate $\lambda$.
I will present my findings showing:
(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 $\lambda$ compared to obscured ones,
(3) the obscured AGN fraction declines sharply at $\log\lambda_{\rm break} \sim-2$ for $z <0.5$, but shifts to higher $\lambda$ values with increasing redshift,
(4) the incidence of AGN within the blow-out region of the $\lambda-N_{\rm H}$ plane increases with redshift.
These observations provide compelling evidence for AGN "downsizing" and for radiation-regulated nuclear-scale obscuration with an increasing host galaxy contribution towards higher redshifts.
Thanks to its wide coverage, eROSITA provides a unique sample of low-redshift AGN located within the blow-out region. Studying the properties of this sample, such as star formation rate, outflow characteristics, and radio detection, can offer valuable insights into the AGN life cycle and its interaction with the host galaxy.
