The XXL Survey XXXII. Spatial clustering of the XXL-S AGN
  The XMM-XXL Survey spans two fields of $\rm 25$ deg$^2$ each observed for
more than 6Ms with XMM, which provided a sample of tens of thousands of point
sources with a flux limit of $\sim 2.2 \times 10^{-15}$ and $\sim 1.4 \times
10^{-14}$ erg s$^{-1}$ cm$^{2}$, corresponding to 50% of the area curve, in the
soft band and hard band, respectively. In this paper we present the spatial
clustering properties of $\sim 3100$ and $\sim 1900$ X-ray active galactic
nuclei (AGNs) in the 0.5-2 and 2-10 keV bands, respectively, which have been
spectroscopically observed with the AAOmega facility. This sample is 90%
redshift complete down to an optical magnitude limit of $r\lesssim 21.8$. The
sources span the redshift interval $0<z<5.2$, although in the current analysis
we limit our samples to $z\le 3$, with corresponding sample median values of
$\bar{z}\simeq 0.96$ and 0.79 for the soft band and hard band, respectively. We
employ the projected two-point correlation function to infer the spatial
clustering and find a correlation length $r_0=7.0 (\pm 0.34)$ and 6.42$(\pm
0.42)$ $h^{-1}$ Mpc, respectively, for the soft- and hard-band detected sources
with a slope for both cases of $\gamma=1.44 (\pm 0.1)$. The power-law
clustering was detected within comoving separations of 1 and $\sim$25 $h^{-1}$
Mpc. These results, as well as those derived in two separate redshift ranges,
provide bias factors of the corresponding AGN host dark matter halos that are
consistent with a halo mass of $\log_{10} [M_h/(h^{-1} M_{\odot})]=13.04\pm
0.06$, confirming the results of most recent studies based on smaller X-ray AGN
samples.
