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Mid-IR Properties of Seyferts: Spitzer IRS Spectroscopy of the IRAS 12 μm Seyfert Sample

Published online by Cambridge University Press:  03 June 2010

Vassilis Charmandaris ,
Yanling Wu ,
Jiasheng Huang ,
Luigi Spinoglio  and
Silvia Tommasin
Vassilis Charmandaris
Affiliation:
University of Crete, Department of Physics, GR-71003, Heraklion, Greece Email: [email protected] IESL/Foundation for Research and Technology - Hellas, GR-71110, Heraklion, Greece, and Chercheur Associé, Observatoire de Paris, F-75014, Paris, France
Yanling Wu
Affiliation:
Infrared Processing and Analysis Center, Caltech, Pasadena, CA 91125, USA
Jiasheng Huang
Affiliation:
Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
Luigi Spinoglio
Affiliation:
Istituto di Fisica dello Spazio Interplanetario, INAF, I-00133 Rome, Italy Dipartimento di Fisica, Universita di Roma, La Sapienza, Rome, Italy
Silvia Tommasin
Affiliation:
Istituto di Fisica dello Spazio Interplanetario, INAF, I-00133 Rome, Italy Dipartimento di Fisica, Universita di Roma, La Sapienza, Rome, Italy
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Abstract

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We performed an analysis of the mid-infrared properties of the 12 μm Seyfert sample, a complete unbiased 12 μm flux limited sample of local Seyfert galaxies selected from the IRAS Faint Source Catalog based on low-resolution spectra obtained with the Infrared Spectrograph (IRS) on-board Spitzer Space Telescope. A detailed presentation of this analysis is discussed by Wu et al. (2009). We find that, on average, the 15–30 μm slope of the continuum is 〈 α15–30〉 = −0.85 ± 0.61 for Seyfert 1s and −1.53 ± 0.84 for Seyfert 2s, and there is substantial scatter in each type. Moreover, nearly 32% of Seyfert 1s, and 9% of Seyfert 2s, display a peak in the mid-infrared spectrum at 20 μm, which is attributed to an additional hot dust component. The polycyclic aromatic hydrocarbon (PAH) equivalent width decreases with increasing dust temperature, as indicated by the global infrared color of the host galaxies. However, no statistical difference in PAH equivalent width is detected between the two Seyfert types of the same bolometric luminosity. Finally, we propose a new method to estimate the AGN contribution to the integrated 12 μm galaxy emission, by subtracting the “star formation” component in the Seyfert galaxies, making use of the tight correlation between PAH 11.2 μm luminosity and 12 μm luminosity for star forming galaxies.

Keywords

galaxies: activegalaxies: Seyfertgalaxies: nucleiinfrared: galaxies
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 5 , Symposium S267: Co-Evolution of Central Black Holes and Galaxies , August 2009 , pp. 254 - 259
Copyright
Copyright © International Astronomical Union 2010

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