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.