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Modeling the Nuclear Infrared Spectral Energy Distribution of Type II Active Galactic Nuclei

Lira, Paulina and Videla, Liza and Wu, Yanling and Alonso-Herrera, Almudena and Alexander, David M. and Ward, Martin (2013) Modeling the Nuclear Infrared Spectral Energy Distribution of Type II Active Galactic Nuclei. Astrophysical Journal, 764 (2). Art. No. 159. ISSN 0004-637X. http://resolver.caltech.edu/CaltechAUTHORS:20130402-083438093

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Abstract

We present results from model fitting to the spectral energy distribution (SED) of a homogeneous sample of Seyfert II galaxies drawn from the 12 μm Galaxy Sample. Imaging and nuclear flux measurements are presented in an accompanying paper. Here we add Spitzer/IRS observations to further constrain the SEDs after careful subtraction of a starburst component. We use the library of CLUMPY torus models from Nenkova et al. and also test the two-phase models recently produced by Stalevski et al. We find that photometric and spectroscopic observations in the mid-IR (λ ≳ 5 μm) are crucial to properly constrain the best-fit torus models. About half of our sources show clear near-IR excess of their SEDs above the best-fit models. This problem can be less severe when using the Stalevski et al. models. The nature of this emission is not clear since best-fitted blackbody temperatures are very high (~1700-2500 K) and the Type II classification of our sources would correspond to a small probability to peer directly into the hottest regions of the torus. Crucially, the derived torus parameters are quite robust when using CLUMPY models, independently of whether or not the sources require an additional blackbody component. Our findings suggest that tori are characterized by N_0 ≳ 5, σ ≳ 40, τ ≾ 25, ∠i ≳ 40°, Y ≾ 50, and A^(los)_v ~ 100-300, where N_0 is the number of clouds in the equatorial plane of the torus, σ is the characteristic opening angle of the cloud distribution, τ is the opacity of a single cloud, ∠i is the line-of-sight orientation of the torus, Y is the ratio of the inner to the outer radii, and A^(los)_v is the total opacity along the line of sight. From these, we can determine typical torus sizes and masses of 0.1-5.0 pc and 10^4-10^6 M_☉, respectively. We find tentative evidence that those nuclei with detected hidden broad-line regions are characterized by lower levels of extinction than those without one. Finally, we find no correlation between the torus properties and the presence of circumnuclear or more global star formation.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1088/0004-637X/764/2/159DOIArticle
http://iopscience.iop.org/0004-637X/764/2/159PublisherArticle
ORCID:
AuthorORCID
Alexander, David M.0000-0002-5896-6313
Additional Information:© 2013 American Astronomical Society. Received 2012 February 20; accepted 2012 December 2; published 2013 February 4. P.L. acknowledges everybody at the Department of Astronomy at the University of Yale for their hospitality during a six month sabbatical period. P.L. also acknowledges Moshe Elitzur and Robert Nikutta from the Department of Astronomy at the Kentucky University, home of the Clumpy code and models, for all their help and guidance. Finally, we are grateful to Patrick Roche and Emeric Le Floc’h for sharing their spectroscopic observations with us. P.L. is grateful for the financial support by Fondecyt grant No. 1080603. L.V. gratefully acknowledges fellowship support by project MECESUP UCH0118, and partial support from Fondecyt project 1080603. This publication was also financed by the ALMA-Conicyt Fund, allocated to the project No. 31060003. A.A.-H. acknowledges support from the Spanish Plan Nacional de Astronomía y Astrofísica under grant AYA2009-05705-E. We are happy to acknowledge the help from the anonymous referee. Finally, this work could not have been possible without the help of A. Cooke.
Funders:
Funding AgencyGrant Number
MECESUPUCH0118
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1080603
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)31060003
Plan Nacional de Astronomía y AstrofísicaAYA2009-05705-E
Subject Keywords:galaxies: Seyfert
Record Number:CaltechAUTHORS:20130402-083438093
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20130402-083438093
Official Citation:Modeling the Nuclear Infrared Spectral Energy Distribution of Type II Active Galactic Nuclei Paulina Lira et al. 2013 ApJ 764 159
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37711
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:02 Apr 2013 16:25
Last Modified:31 Oct 2017 21:32

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