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

Brivael Laloux*, Antonis Georgakakis*, David M. Alexander, Johannes Buchner, Carolina Andonie, Nischal Acharya, James Aird, Alba V. Alonso-Tetilla, Angela Bongiorno, Ryan C. Hickox, Andrea Lapi, Blessing Musiimenta, Cristina Ramos Almeida, Carolin Vellforth, Francesco Shankar

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

We adopt a Bayesian X-ray spectral approach to investigate the accretion properties of unobscured (20 < log(NH /cm−2 < 22) and obscured (22 < log(NH /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, LX , obscuring column densities, NH , and specific accretion rates λ ∝ LX /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 NH 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 λ compared 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 λ values with increasing redshift, (4) the incidence of AGN within the theoretically unstable blow-out region of the λ − NH 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.
Original languageEnglish
Pages (from-to)3459-3479
Number of pages21
JournalMonthly Notices of the Royal Astronomical Society
Volume532
Issue number3
Early online date4 Jul 2024
DOIs
Publication statusPublished - 1 Aug 2024

Keywords / Materials (for Non-textual outputs)

  • galaxies: active
  • X-rays: galaxies - infrared
  • galaxies

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