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

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 (N H/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.

The Astrophysical Journal, Volume 871, Issue 2, article id. 240 (2019)

Authors: 
Ananna, Tonima Tasnim; Treister, Ezequiel; Urry, C. Megan; Ricci, C.; Kirkpatrick, Allison*; LaMassa, Stephanie; Buchner, Johannes; Civano, Francesca; Tremmel, Michael; Marchesi, Stefano *KU Author