The clustering of X-ray AGN at 0.5 < z < 4.5: host galaxies dictate dark
  matter halo mass
  We present evidence that AGN do not reside in ``special'' environments, but
instead show large-scale clustering determined by the properties of their host
galaxies. Our study is based on an angular cross-correlation analysis applied
to X-ray selected AGN in the COSMOS and UDS fields, spanning redshifts from
$z\sim4.5$ to $z\sim0.5$. Consistent with previous studies, we find that AGN at
all epochs are on average hosted by galaxies in dark matter halos of
$10^{12}-10^{13}$ M$_{\odot}$, intermediate between star-forming and passive
galaxies. We find, however, that the same clustering signal can be produced by
inactive (i.e. non-AGN) galaxies closely matched to the AGN in spectral class,
stellar mass and redshift. We therefore argue that the inferred bias for AGN
lies in between the star-forming and passive galaxy populations because AGN
host galaxies are comprised of a mixture of the two populations. Although AGN
hosted by higher mass galaxies are more clustered than lower mass galaxies,
this stellar mass dependence disappears when passive host galaxies are removed.
The strength of clustering is also largely independent of AGN X-ray luminosity.
We conclude that the most important property that determines the clustering in
a given AGN population is the fraction of passive host galaxies. We also infer
that AGN luminosity is likely not driven by environmental triggering, and
further hypothesise that AGN may be a stochastic phenomenon without a strong
dependence on environment.
