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Nuclear Infrared Spectral Energy Distribution of Type II Active Galactic Nuclei

Videla, L.; Lira, P.; Andrews, H.; Alonso-Herrero, A.; Alexander, D.M.; Ward, M.

Nuclear Infrared Spectral Energy Distribution of Type II Active Galactic Nuclei Thumbnail


Authors

L. Videla

P. Lira

H. Andrews

A. Alonso-Herrero



Abstract

We present near- and mid-IR observations of a sample of Seyfert II galaxies drawn from the 12 μm 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 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 active galactic nuclei (AGNs) and H II 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 α < 1 for an SED characterized as λf λvpropλα. The three objects with an H II nucleus and two Seyfert nuclei with strong contamination from a circumnuclear also show an upturn. For genuine AGNs, 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.

Journal Article Type Article
Publication Date Feb 1, 2013
Deposit Date May 29, 2014
Publicly Available Date Aug 12, 2014
Journal Astrophysical Journal Supplement
Print ISSN 0067-0049
Electronic ISSN 1538-4365
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 204
Issue 2
DOI https://doi.org/10.1088/0067-0049/204/2/23
Public URL https://durham-repository.worktribe.com/output/1452165

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Copyright Statement
© 2013. The American Astronomical Society. All rights reserved. Printed in the U.S.A.






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