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