Galaxy properties of type 1 and 2 X-ray selected AGN and comparison
  among different classification criteria
  We present analyses of host galaxy properties of type 1 and type 2 X-ray
selected AGNs in the XMM-XXL field, which have available optical spectroscopic
classification. We model their optical to far-infrared spectral energy
distributions (SEDs) using the X-CIGALE code. X-CIGALE allows the fitting of
X-ray flux and accounts for the viewing angle of dusty torus and the
attenuation from polar dust. By selecting matched type 1 and 2 subsamples in
the X-ray luminosity and redshift parameter space, we find that both types live
in galaxies with similar star formation. However, type 2 AGN tend to reside in
more massive systems ($10.87^{+0.06}_{-0.12}\,\rm M_\odot$) compared to their
type 1 counterparts ($10.57^{+0.20}_{-0.12}\,\rm M_\odot$). In the second part
of our analysis, we compare the spectroscopic classification with that from the
SED fitting. X-CIGALE successfully identifies all spectroscopic type 2 sources
either by estimating an inclination angle that corresponds to edge on viewing
of the source or by measuring increased polar dust in these systems. $\sim
85\%$ of spectroscopic type 1 AGN are also identified as such, based on the SED
fitting analysis. There is a small number of sources ($\sim 15\%$ of the
sample), that present broad lines in their spectra, but show strong indications
of obscuration, based on SED analysis. These, could be systems that are viewed
face on and have an extended dust component along the polar direction. The
performance of X-CIGALE in classifying AGN is similar at low and high
redshifts, under the condition that there is sufficient photometric coverage.
Finally, usage of optical/mid-IR colour criteria to identify optical red AGN
(${\it{u}}-\rm W3$), suggests that these criteria are better suited for IR
selected AGN and their efficiency drops for the low to moderate luminosity
sources included in X-ray samples.
