The Detection of Silicate Emission from Quasars at 10 and 18 Microns

Lei Hao (1) , Henrik W. W. Spoon (1) , G. C. Sloan (1) , J. A. Marshall (1) , Lee Armus (2) , A. Tielens (3) , B. Sargent (4) , Ilse van Bemmel (5) , Vassilis Charmandaris (1, 6) , Dan W. Weedman (1) , J. R. Houck (1)

1 Department of Astronomy, Cornell University
2 SSC - Spitzer Science Center, California Institute of Technology
3 SRON National Institute for Space Research and Kapteyn Institute
4 Department of Physics and Astronomy, University of Rochester
5 STScI - Space Telescope Science Institute
6 LERMA - Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique

We report the spectroscopic detection of silicate emission at 10 and 18 mum in five PG quasars, the first detection of these two features in galaxies outside the Local Group. This finding is consistent with the unification model for active galactic nuclei (AGNs), which predicts that an AGN torus seen pole-on should show a silicate emission feature in the mid-infrared. The strengths of the detected silicate emission features range from 0.12 to 1.25 times the continuum at 10 mum and from 0.20 to 0.79 times the continuum at 18 mum. The silicate grain temperatures inferred from the ratio of 18 mum to 10 mum silicate features under the assumption of optically thin emission range from 140 to 220 K.

Domaines: Astrophysique [astro-ph]

Lei Hao, Henrik W. W. Spoon, G. C. Sloan, J. A. Marshall, Lee Armus, et al.. The Detection of Silicate Emission from Quasars at 10 and 18 Microns. The Astrophysical journal letters, 2005, 625, pp.L75-L78. ⟨10.1086/431227⟩. ⟨hal-03786082⟩