AGN Dusty Tori. II. Observational Implications of Clumpiness
- Seneca College, 1750 Finch Avenue East, Toronto, ON M2J 2X5 (Canada)
- Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506-0055 (United States)
- Department of Astronomy, University of Washington, Seattle, WA 98105 (United States)
Clumpy torus models with N{sub 0} {approx} 5-15 dusty clouds along radial equatorial rays successfully explain AGN infrared observations. The dust has standard Galactic composition, with individual cloud optical depth {tau}{sub V} {approx} 30-100 at visual. The models naturally explain the observed behavior of the 10 {mu}m silicate feature, in particular the lack of deep absorption features in AGNs of any type, and can reproduce the weak emission feature tentatively detected in type 2 QSOs. The clouds' angular distribution must have a soft edge, e.g., Gaussian, and the radial distribution should decrease as 1/r or 1/r{sup 2}. In line with recent interferometry, the ratio of the torus outer to inner radius can be as small as {approx}5-10. The models can produce nearly isotropic IR emission together with highly anisotropic obscuration, as required by observations. Clumpiness implies that the viewing angle determines an AGN classification only probabilistically; a source can display type 1 properties even from directions close to the equatorial plane. The fraction of obscured sources depends not only on the torus angular thickness but also on the cloud number N{sub 0}, and this fraction's observed decrease with luminosity can be explained with a decrease of either parameter. X-ray obscuration, too, is probabilistic; resulting from both dusty and dust-free clouds, it might be dominated by the latter, giving rise to the observed QSOs that are X-ray obscured. Observations indicate that the torus and broad-line-emitting clouds form a seamless distribution, with the transition between the two caused by dust sublimation. Torus clouds may have been detected in the outflow component of H{sub 2}O maser emission from two AGNs. Proper-motion measurements of outflow masers, especially in Circinus, are a promising method for probing the morphology and kinematics of torus clouds.
- OSTI ID:
- 21565480
- Journal Information:
- Astrophysical Journal, Vol. 685, Issue 1; Other Information: DOI: 10.1086/590483; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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