Polar dust obscuration in broad-line active galaxies from the XMM-XXL
  field
  Dust is observed in the polar regions of nearby AGN and it is known to
contribute substantially to their mid-IR emission and to the obscuration of
their UV to optical emission. We selected a sample of 1275 BLAGN in the XMM-XXL
field, with optical to infrared photometric data. These AGN are seen along
their polar direction and we expect a maximal impact of dust located around the
poles when it is present. We used X-CIGALE, which introduces a dust component
to account for obscuration along the polar directions, modeled as a foreground
screen, and an extinction curve that is chosen as it steepens significantly at
short wavelengths or is much grayer. By comparing the results of different
fits, we are able to define subsamples of sources with positive statistical
evidence in favor of or against polar obscuration and described using the gray
or steep extinction curve.
  We find a similar fraction of sources with positive evidence for and against
polar dust. Applying statistical corrections, we estimate that half of our
sample could contain polar dust and among them, 60% exhibit a steep extinction
curve and 40% a flat extinction curve; although these latter percentages are
found to depend on the adopted extinction curves. The obscuration in the V-band
is not found to correlate with the X-ray column density, while A_V/N_H ratios
span a large range of values and higher dust temperatures are found with the
flat, rather than with the steep extinction curve. Ignoring this polar dust
component in the fit of the spectral energy distribution of these composite
systems leads to an overestimation of the stellar contribution. A single fit
with a polar dust component described with an SMC extinction curve efficiently
overcomes this issue but it fails at identifying all the AGN with polar dust
obscuration.
