Dust Emission from Active Galactic Nuclei

Unified schemes of active galactic nuclei require an obscuring dusty torus around the central source, giving rise to a Seyfert 1 line spectrum for pole-on viewing and Seyfert 2 characteristics in edge-on sources. Although the observed IR is in broad agreement with this scheme, the behavior of the 10 μm silicate feature and the width of the far-IR emission peak remained serious problems in all previous modeling efforts. We show that these problems find a natural explanation if the dust is contained in approximately five to 10 clouds along radial rays through the torus. The spectral energy distributions of both type 1 and type 2 sources are properly reproduced from different viewpoints of the same object if the optical depth of each cloud is 60 at visual wavelengths and if the clouds' mean free path increases roughly in proportion to the radial distance.

[1]  A. Marconi,et al.  Dust in active nuclei. I. evidence for anomalous properties , 2000, astro-ph/0010009.

[2]  G. Rieke,et al.  The infrared spectrum of NGC 1068 , 1975 .

[3]  G. Neugebauer,et al.  Continuum energy distribution of quasars: Shapes and origins , 1989 .

[4]  G. Matt,et al.  X-ray absorption in Seyfert 2 galaxies , 2001 .

[5]  R. Della Ceca,et al.  A Three-dimensional Diagnostic Diagram for Seyfert 2 Galaxies: Probing X-Ray Absorption and Compton Thickness , 1998, astro-ph/9811074.

[6]  User Manual for DUSTY , 1999, astro-ph/9910475.

[7]  N. Panagia,et al.  Extinction in inhomogeneous clouds. , 1984 .

[8]  Ari Laor,et al.  Spectroscopic constraints on the properties of dust in active galactic nuclei , 1993 .

[9]  P. Roche,et al.  An atlas of mid-infrared spectra of galaxy nuclei , 1991 .

[10]  S. Ueno,et al.  The 9.7 Micron Silicate Dust Absorption toward the Cygnus A Nucleus and the Inferred Location of the Obscuring Dust , 2000, astro-ph/0001321.

[11]  Michael Rowan-Robinson,et al.  A new model for the infrared emission of quasars , 1995 .

[12]  Julian H. Krolik,et al.  Infrared Spectra of Obscuring Dust Tori around Active Galactic Nuclei. II. Comparison with Observations , 1993 .

[13]  Robert Antonucci,et al.  Unified models for active galactic nuclei and quasars , 1993 .

[14]  Julian H. Krolik,et al.  Infrared spectra of obscuring dust tori around active galactic nuclei. I - Calculational method and basic trends , 1992 .

[15]  L. Danese,et al.  Thick tori around active galactic nuclei: a comparison of model predictions with observations of the infrared continuum and silicate features , 1994 .

[16]  J. Hough,et al.  Observations and a model for the infrared continuum of Centaurus A , 1999 .

[17]  Alberto Franceschini,et al.  Thick Tori around Active Galactic Nuclei: The Case for Extended Tori and Consequences for Their X-Ray and Infrared Emission , 1997 .

[18]  M. S. Oey,et al.  Atlas of quasar energy distributions , 1994 .

[19]  A. Kinney,et al.  Testing the Unified Model with an Infrared-selected Sample of Seyfert Galaxies , 2001, astro-ph/0103263.