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Date and Time of the Query: 2019-04-19 T19:48:53 PDT
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For refcode 2007ApJ...671..124D:
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Copyright by American Astronomical Society. Reproduced by permission
2007ApJ...671..124D Spitzer IRS Observations of Seyfert 1.8 and 1.9 Galaxies: A Comparison with Seyfert 1 and Seyfert 2 Deo, R. P.; Crenshaw, D. M.; Kraemer, S. B.; Dietrich, M.; Elitzur, M.; Teplitz, H.; Turner, T. J. Abstract. We present Spitzer mid-infrared spectra of 12 Seyfert 1.8 and 1.9 galaxies over the 5-38 micron 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 micron 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 micron 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 micron 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 micron correlates strongly with the 20-30 micron 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 micron. The strengths of the high-ionization forbidden narrow emission lines [O IV] 25.89 micron, [Ne III] 15.56 micron, and [Ne V] 14.32 micron relative to [Ne II] 12.81 micron 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. Key words: ISM: Dust, Extinction, Galaxies: Active, Galaxies: Seyfert
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