The Nature of Obscuration in AGN: I. Insights from Host Galaxies
  We analyze a sample of 30,000 nearby obscured AGNs with optical spectra from
SDSS and mid-IR photometry from WISE. Our aim is to investigate the AGN host
galaxy properties with mid-IR luminosities as AGN activity indicator, and to
compare with previous studies based on [OIII] emission lines. First we find
that the [3.4] - [4.6] colour has weak dependence on host stellar age, but
strong dependence on AGN activity. We then use a "pair-matching" technique to
subtract the host 4.6 micron contribution. By combining Seyferts with a sample
of SDSS quasars at z < 0.7, we show that the [OIII] and the intrinsic AGN 4.6
micron luminosities correlate roughly linearly over 4 orders of magnitude, but
with substantial scatter. We also compare the partition functions of the total
integrated 4.6 micron and [OIII] line luminosities from Seyferts and a
sub-population of LINERs with significant nuclear 4.6 micron emission, as
function of a variety of host galaxy properties, finding that they are
identical. We conclude, therefore, that [OIII] as an AGN indicator shows no
particular biases as compared to the 4.6 micron luminosity. Our results also
demonstrate that some LINERs do fit in with the expectations of the simple
Unified Model.
