Deo, R. P. and Crenshaw, D. M. and Kraemer, S. B. and Dietrich, M. and Elitzur, M. and Teplitz, H. and Turner, T. J. (2007) Spitzer IRS Observations of Seyfert 1.8 and 1.9 Galaxies: A Comparison with Seyfert 1 and Seyfert 2. Astrophysical Journal, 671 (1). pp. 124-135. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20091109-100046575
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We present Spitzer mid-infrared spectra of 12 Seyfert 1.8 and 1.9 galaxies over the 5-38 μm region. We compare the spectral characteristics of this sample to those of 58 Seyfert 1 and 2 galaxies from the Spitzer archives. An analysis of the spectral shapes, the silicate 10 μm feature and the emission-line fluxes have enabled us to characterize the mid-IR properties of Seyfert 1.8/1.9s. We find that the EWs of the 10 μm silicate feature are generally weak in all Seyfert galaxies, as previously reported by several studies. The few Seyfert galaxies in this sample that show deep 10 μm silicate absorption features are highly inclined and/or merging galaxies. It is likely that these absorption features originate primarily in the dusty interstellar medium of the host galaxy rather than in a dusty torus on parsec scales close to the central engine. We find that the EW of the PAH band at 6.2 μm correlates strongly with the 20-30 μm spectral index. Either of these quantities is a good indicator of the amount of starburst contribution to the mid-IR spectra. The spectra of Seyfert 1.8s and 1.9s are dominated by these starburst features, similar to most Seyfert 2s. They show strong PAH bands and a strong red continuum toward 30 μm. The strengths of the high-ionization forbidden narrow emission lines [O IV] 25.89 μm, [Ne III] 15.56 μm, and [Ne V] 14.32 μm relative to [Ne II] 12.81 μm are weaker in Seyfert 1.8/1.9s and Seyfert 2s than in Seyfert 1s. The weakness of high-ionization lines in Seyfert 1.8-1.9s is suggestive of intrinsically weak AGN continua and/or stronger star formation activity leading to enhanced [Ne II]. We discuss the implications of these observational results in the context of the unified model of AGNs.
|Additional Information:||© 2007 The American Astronomical Society. Received 2007 April 27; accepted 2007 August 28. This work is based in part on observations made with the Spitzer Space Telescope and in part on archival data obtained with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory (JPL), California Institute of Technology, under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL. This research has made use of the NASA / IPAC Extragalactic Database (NED), which is operated by JPL, under contract with the National Aeronautics and Space Administration. This research has also made use of NASA’s Astrophysics Data System Bibliographic Services. Facilities: Spitzer|
|Subject Keywords:||dust, extinction; galaxies : active; galaxies : Seyfert|
|Official Citation:||Spitzer IRS Observations of Seyfert 1.8 and 1.9 Galaxies: A Comparison with Seyfert 1 and Seyfert 2 R. P. Deo, D. M. Crenshaw, S. B. Kraemer, M. Dietrich, M. Elitzur, H. Teplitz, and T. J. Turner 2007 ApJ 671 124-135 doi: 10.1086/522823|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||25 Nov 2009 20:05|
|Last Modified:||26 Dec 2012 11:32|
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