Properties of dusty tori in active galactic nuclei – II. Type 2 AGN
- Creators
- Hatziminaoglou, E.
- Fritz, J.
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Jarrett, T. H.
Abstract
This paper is the second part of a work investigating the properties of dusty tori in active galactic nuclei (AGN) by means of multicomponent spectral energy distribution (SED) fitting. It focuses on low-luminosity, low-redshift (z ≤ 0.25) AGN selected among emission line galaxies in the overlapping regions between Spitzer Wide-area Infrared Extragalactic Survey (SWIRE) and Sloan Digital Sky Survey Data Release 4 as well as X-ray, radio and mid-infrared selected type 2 AGN samples from the literature. The available multiband photometry covers the spectral range from the u band up to 160 μm. Using a standard χ^2 minimization, the observed SED of each object is fit to a set of multicomponent models comprising a stellar component, a high optical depth (τ_(9.7) ≥ 1.0) torus and cold emission from a starburst (SB). The torus components assigned to the majority of the objects were those of the highest optical depth of our grid of models (τ_(9.7) = 10.0). The contribution of the various components (stars, torus, SB) is reflected in the position of the objects on the Infrared Array Camera (IRAC) colour diagram, with star-, torus- and SB-dominated objects occupying specific areas of the diagrams and composite objects lying in between. The comparison of type 1 (as derived from Hatziminaoglou et al.) and type 2 AGN properties is broadly consistent with the unified scheme. The estimated ratio between type 2 and 1 objects is about 2–2.5:1. The AGN accretion-to-infrared luminosity ratio is an indicator of the obscuration of the AGN since it scales down with the covering factor. We find evidence supporting the receding torus paradigm, with the estimated fraction of obscured AGN, derived from the distribution of the covering factor, decreasing with increasing optical luminosity (λL_(5100)) over four orders of magnitude. The average star formation rates (SFRs) are of ~10 M_⊙ yr^(−1) for the low-z sample, ~40 M_⊙ yr^(−1) for the other type 2 AGN and ~115 M_⊙ yr^(−1) for the quasars; this result however, might simply reflect observational biases, as the quasars under study were one to two orders of magnitude more luminous than the various type 2 AGN. For the large majority of objects with 70 and/or 160 μm detections, an SB component was needed in order to reproduce the data points, implying that the far-infrared emission in AGN arises mostly from star formation; moreover, the SB-to-AGN luminosity ratio shows a slight trend with increasing luminosity.
Additional Information
© 2009 The Authors. Journal compilation © 2009 RAS. Accepted 2009 July 13. Received 2009 July 13; in original form 2009 May 5. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. Support for this work, part of the Spitzer Space Telescope Legacy Science Programme, was provided by NASA through an award issued by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. Funding for the creation and distribution of the SDSS Archive has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Aeronautics and Space Administration, the National Science Foundation, the U.S. Department of Energy, the Japanese Monbukagakusho and the Max Planck Society. The SDSS web site is http://www.sdss.org/. This publication makes use of data products from the 2MASS, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This work made use of Virtual Observatory tools and services, namely TOPCAT (http://www.star.bris.ac.uk/mbt/topcat/) and VizieR (http://vizier.u-strasbg.fr/cgi-bin/VizieR). We would like to thank R. Maiolino for kindly providing material for Fig. 19. We would also like to thank the anonymous referee for their in-depth study of the paper and the subsequent comments that, we believe, greatly improved the manuscript. SUPPORTING INFORMATION Additional Supporting Information may be found in the online version of this article: Table 1. SDSS names, coordinates, redshifts, emission line properties and stellar masses for the 420 objects overlapping the SWIRE fields and the narrow emission line object catalogue from Kauffmann et al. (2003). Table 2. SWIRE fluxes of the sample presented in Table 1. Table 3. COSMOS names, coordinates, redshifts and classification type for the COSMOS type 2 AGN sample, from Trump et al. (2007). Table 4.COSMOSSpitzer fluxes of the sample presented in Table 3. Figure 5. Best-fitting SEDs for the low-z objects with reduced χ2 < 16.0 that were assigned a torus component. Figure 14. The best fits for the COSMOS objects with reduced χ2 < 16.0 that were assigned a torus component. Figure 15. The best fits for the ELAIS AGN with reduced χ2 < 16.0 that were assigned a torus component.Attached Files
Published - Hatziminaoglou2009p6211Mon_Not_R_Astron_Soc.pdf
Supplemental Material - sm001.zip
Supplemental Material - sm002.zip
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Additional details
- Eprint ID
- 16610
- Resolver ID
- CaltechAUTHORS:20091106-151756929
- 1407
- NASA
- Alfred P. Sloan Foundation
- NASA
- NSF
- U.S. Department of Energy
- Japanese Monbukagakusho
- Max Planck Society
- Created
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2009-11-16Created from EPrint's datestamp field
- Updated
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2021-11-08Created from EPrint's last_modified field