The XXL Survey XIX. A realistic population of simulated X-ray AGN: Comparison of models with observations

TL;DR

This study uses cosmological simulations to generate realistic synthetic X-ray AGN catalogs, successfully matching observed properties like luminosity functions, Eddington ratios, and clustering, thereby validating the simulation models.

Contribution

The paper introduces a method to produce synthetic X-ray AGN catalogs from simulations that accurately reproduce multiple observed AGN demographics.

Findings

Simulated AGN accurately reproduce the observed X-ray luminosity function.

Synthetic catalogs match observed Eddington ratio distributions.

Clustering properties of simulated AGN align with observations.

Abstract

Modern cosmological simulations rely heavily on feedback from active galactic nuclei (AGN) in order to stave off overcooling in massive galaxies and galaxy groups and clusters. An important independent test is whether or not the simulations capture the broad demographics of the observed AGN population. Here, we have used the cosmo-OWLS suite of cosmological hydrodynamical simulations to produce realistic synthetic catalogs of X-ray AGN out to $z$=3, with the aim of comparing the catalogs to the observed X-ray AGN population in the XXL survey and other recent surveys. We focused on the unabsorbed X-ray luminosity function (XLF), the Eddington ratio distribution, the black hole mass function, and the projected clustering of X-ray AGN. To compute the unabsorbed XLF of the simulated AGN, we used recent empirically-determined bolometric corrections. We show that the simulated AGN sample accurately reproduces the observed XLF over 3 orders of magnitude in X-ray luminosity in all redshift bins. To compare to the observed Eddington ratio distribution and the clustering of AGN, we produced detailed 'XMM-Newton-detected' catalogs of the simulated AGN. This requires the production of synthetic X-ray images extracted from light cones of the simulations that fold in the relevant instrumental effects of XMM-Newton. We apply a luminosity- and redshift-dependent obscuration function for the AGN and employ the same AGN detection algorithm as used for the real XXL survey. We demonstrate that the detected population of simulated AGN reproduces the observed Eddington ratio distribution and projected clustering from XXL quite well. We conclude that the simulations have a broadly realistic population of AGN and that our synthetic X-ray AGN catalogs should be useful for interpreting additional trends and as a helpful tool for quantifying AGN contamination in galaxy group and cluster X-ray surveys.