Dr. Brivael Laloux (INAF/Capodimonte)
8 January 2025
11:30, Aula Piazzi
Abstract:
Accreting supermassive black holes, or active galactic nuclei (AGN), grow behind obscuring clouds of gas and dust. Orientation unification models suggest obscured and unobscured AGN differ only by viewing angle, while evolutionary models propose obscuration as a life-cycle phase, predicting different accretion properties. We analysed 3882 X-ray-selected AGN from three Chandra deep fields, constraining their stellar masses, intrinsic X-ray luminosities, obscuration levels, and specific accretion rates (λ∝LX/M⋆). Using a Bayesian non-parametric approach, we derived the specific accretion rate distribution (SARD) for obscured and unobscured AGN to z≈3. Our results show: 1) both SARDs share similar shapes, shifting towards higher accretion rates with redshift; 2) unobscured SARDs are shifted to higher λ compared to obscured ones; 3) the obscured AGN fraction declines sharply at logλ~-2 for z<0.5 but shifts to higher λ with redshift; 4) AGN in the blow-out region of the λ−NH plane increase with redshift. These findings support AGN “downsizing” and radiation-regulated obscuration nuclear-scale obscuration with an increasing host galaxy contribution towards higher redshifts. Additionally, the Euclid space telescope, launched in July 2023, provides unprecedented near-infrared data. Using Euclid’s observations, I developed an SED fitting methodology to measure stellar masses and reliability factors for thousands of AGN host galaxies.