Extended silicate dust emission in palomar-green QSOs

M. Schweitzer, B. Groves, H. Netzer, D. Lutz, E. Sturm, A. Contursi, R. Genzel, L. J. Tacconi, S. Veilleux, D. C. Kim, D. Rupke, A. J. Baker

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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.

Original languageEnglish (US)
Pages (from-to)101-117
Number of pages17
JournalAstrophysical Journal
Issue number1
StatePublished - May 20 2008

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Galaxies: active
  • Infrared: galaxies
  • Quasars: general


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