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Title:
Extended Silicate Dust Emission in Palomar-Green QSOs
Authors:
Schweitzer, M.; Groves, B.; Netzer, H.; Lutz, D.; Sturm, E.; Contursi, A.; Genzel, R.; Tacconi, L. J.; Veilleux, S.; Kim, D.-C.; Rupke, D.; Baker, A. J.
Affiliation:
AA(Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany; ), AB(Leiden University, Niels Bohrweg 2, Leiden 2333-CA, Netherlands; ), AC(School of Physics and Astronomy and the Wise Observatory, The Raymond and Beverly Sackler Faculty of Exact Science, Tel-Aviv University, Tel-Aviv 69978, Israel; ), AD(Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany; , , , , ), AE(Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany; , , , , ), AF(Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany; , , , , ), AG(Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany; , , , , ), AH(Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany; , , , , ), AI(Department of Astronomy, University of Maryland, College Park, MD 20742-2421), AJ(Department of Astronomy, University of Maryland, College Park, MD 20742-2421), AK(Department of Astronomy, University of Maryland, College Park, MD 20742-2421), AL(Department of Physics and Astronomy, Rutgers, the State University of New Jersey, 136 Frelinghuysen Road, Piscataway, NJ 08854-8019 )
Publication:
The Astrophysical Journal, Volume 679, Issue 1, pp. 101-117. (ApJ Homepage)
Publication Date:
05/2008
Origin:
UCP
ApJ Keywords:
Galaxies: Active, Infrared: Galaxies, Galaxies: Quasars: General
DOI:
10.1086/587097
Bibliographic Code:
2008ApJ...679..101S

Abstract

This paper addresses the origin of the silicate emission observed in PG QSOs, based on observations with the Spitzer Space Telescope. Scenarios based on the unified model suggest that silicate emission in AGNs arises mainly from the illuminated faces of the clouds in the torus at temperatures near sublimation. However, detections of silicate emission in type 2 QSOs, and the estimated cool dust temperatures, argue for a more extended emission region. To investigate this issue we present the mid-infrared spectra of 23 QSOs. These spectra, and especially the silicate emission features at ~10 and ~18 μm, can be fitted using dusty narrow-line region (NLR) models and a combination of blackbodies. The bolometric luminosities of the QSOs allow us to derive the radial distances and covering factors for the silicate-emitting dust. The inferred radii are 100-200 times larger than the dust sublimation radius, much larger than the expected dimensions of the inner torus. Our QSO mid-IR spectra are consistent with the bulk of the silicate dust emission arising from the dust in the innermost parts of the NLR.
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