We analyse the mid-infrared (MIR) spectra of 39 Seyfert galaxies observed with the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. Our sample consists of 19 Seyfert type 1 (Sy1) galaxies, three intermediate Seyfert galaxies and 17 type 2 Seyfert (Sy2) galaxies in the nearby Universe. This sample was extracted from a larger sample, the circumgalactic environment of which was studied in a previous work by Dultzin-Hacyan et al., who found that Sy2 objects are in interaction more frequently than normal galaxies, while Sy1s are not. In this article, we study the silicate dust distribution that dominates the mid-infrared (MIR) spectra. This dust produces spectral features at 10 and 18 μm that are sensitive to the clumpiness of the dust. We measure the strength of the emission or absorption of the silicate features to find whether there is a correlation between the clumpiness of the circumnuclear dust and the active galactic nucleus (AGN) type and incidence of companions. All isolated Sy1 galaxies have clumpy dust distributions, whereas Sy1s with a close companion can have either clumpy or smooth distributions. In the case of Sy2 galaxies, those with one or more companions have mostly smooth dust distributions, whereas isolated Sy2s may have clumpy or smoothly distributed dust. Our result is at odds with the simplest formulation of the unified scheme for Seyferts and supports an evolutionary sequence where the influence of an interaction triggers a type 2 AGN, which evolves into a type 1.
Digital Object Identifier (DOI)
SMC acknowledges a graduate student scholarship from CONACYT. DD acknowledges support from grant IN107313 from PAPIIT, UNAM. This work is based on observations made with the SpitzerSpace Telescope and has made use of the NASA/IPAC Extragalactic Database, both of which are operated by the Jet Propulsion Laboratory, California Institute of Technology, under contracts with NASA. Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England.
This work is based on observations made with the SpitzerSpace Telescope and has made use of the NASA/IPAC Extragalactic Database, both of which are operated by the Jet Propulsion Laboratory, California Institute of Technology, under contracts with NASA.
The SDSS Web Site is http://www.sdss.org/.
The SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions. The Participating Institutions are the American Museum of Natural History, Astrophysical Institute Potsdam, University of Basel, University of Cambridge, Case Western Reserve University, University of Chicago, Drexel University, Fermilab, the Institute for Advanced Study, the Japan Participation Group, Johns Hopkins University, the Joint Institute for Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and Cosmology, the Korean Scientist Group, the Chinese Academy of Sciences (LAMOST), Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, Ohio State University, University of Pittsburgh, University of Portsmouth, Princeton University, the United States Naval Observatory, and the University of Washington.
Mendoza-Castrejón, S.; Dultzin, D.; Krongold, Y.; González, J. J.; and Elitzur, Moshe, "The Dust Geometric Distribution in Seyfert 1 and Seyfert 2 Galaxies, Isolated and in Interaction" (2015). Physics and Astronomy Faculty Publications. 271.
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