The Accretion History of AGNs. I. Supermassive Black Hole Population Synthesis Model

• Published in: The Astrophysical journal 2019-02, Vol.871 (2), p.240
• Main Authors: Tasnim Ananna, Tonima, Treister, Ezequiel, Megan Urry, C., Ricci, C., Kirkpatrick, Allison, LaMassa, Stephanie, Buchner, Johannes, Civano, Francesca, Tremmel, Michael, Marchesi, Stefano
• Format: Article
• Language: English
• Subjects: Active galactic nuclei; Astrophysics; Black holes; Constraint modelling; Cosmic x rays; Deposition; Emission; galaxies: active; Galaxy: center; Galaxy: evolution; Luminosity; methods: data analysis; Neural networks; Polls & surveys; Population; quasars: supermassive black holes; Supermassive black holes; Synthesis; X-ray emissions; X-rays; X-rays: diffuse background; XMM (spacecraft)
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/aafb77

As matter accretes onto the central supermassive black holes in active galactic nuclei (AGNs), X-rays are emitted. We present a population synthesis model that accounts for the summed X-ray emission from growing black holes; modulo the efficiency of converting mass to X-rays, this is effectively a record of the accreted mass. We need this population synthesis model to reproduce observed constraints from X-ray surveys: the X-ray number counts, the observed fraction of Compton-thick AGNs [log (NH/cm−2) > 24], and the spectrum of the cosmic X-ray background (CXB), after accounting for selection biases. Over the past decade, X-ray surveys by XMM-Newton, Chandra, NuSTAR, and Swift-BAT have provided greatly improved observational constraints. We find that no existing X-ray luminosity function (XLF) consistently reproduces all these observations. We take the uncertainty in AGN spectra into account and use a neural network to compute an XLF that fits all observed constraints, including observed Compton-thick number counts and fractions. This new population synthesis model suggests that, intrinsically, 50% 9% (56% 7%) of all AGNs within z 0.1 (1.0) are Compton-thick.