Nuclear Infrared Spectral Energy Distribution of Type II Active Galactic Nuclei. (arXiv:1301.7000v1 [astro-ph.CO])

Nuclear Infrared Spectral Energy Distribution of Type II Active Galactic Nuclei. (arXiv:1301.7000v1 [astro-ph.CO]):
We present near and mid--IR observations of a sample of Seyfert II galaxies
drawn from the $12\mu$m Galaxy Sample. The sample was observed in the J, H, K,
L, M and N bands. Galaxy Surface Brightness Profiles are modeled using nuclear,
bulge, bar (when necessary) and disk components. To check the reliability of
our findings the procedure was tested using {\em Spitzer\/} observations of
M\,31. Nuclear Spectral Energy Distributions (SEDs) are determined for 34
objects, and optical spectra are presented for 38, including analysis of their
stellar populations using the STARLIGHT spectral synthesis code. Emission line
diagnostic-diagrams are used to discriminate between genuine AGN and HII
nuclei. Combining our observations with those found in the literature, we have
a total of 40 SEDs. It is found that about 40\%\ of the SEDs are characterized
by an upturn in the near-IR, which we have quantified as a NIR slope $\alpha <
1$ for an SED characterized as $\lambda f_{\lambda} \propto \lambda^{\alpha}$.
Three objects with an HII nucleus and two Seyfert nuclei with strong
contamination from a circumnuclear starburst, also show an upturn. For genuine
AGN this component could be explained as emission from the accretion disk, a
jet, or from a very hot dust component leaking from the central region through
a clumpy obscuring structure. The presence of a very compact nuclear starburst
as the origin for this NIR excess emission is not favored by our spectroscopic
data for these objects.


RKS Note: Issue here is distinguishing true AGN from starbursts or H II regions, which can be done in part in the IR as well as in X-ray bands.