Probing the Dusty Accretion Torus of Seyfert Galaxies

Abstract

We show that the IRAS colors of Seyfert galaxies can be understood in terms of a model in which we see emission by hot dust near its sublimation temperature emitting a spectrum that varies little from object to object. For objects observed through the dusty accretion torus, which is optically thick at 12 μm, this dust emission is absorbed to various degrees. In addition, in many objects, this spectrum is veiled by a component produced by a circumnuclear starburst. The hidden broad-line objects all lie along the reddening line in IRAS color-color plots, and the dust extinction at 12 μm lies in the range 0.5-2.5, which implies an H I column density of ~5 × 1022 cm-2 for the hot circumnuclear dust located at about 3 pc from the central engine. For these objects we can also estimate the true luminosities of the central active nuclei from the dereddened IR fluxes. If the simple accretion flow model is correct, then typical accretion rates are on the order of 10 M☉ yr-1. The radiation pressure of the central active galactic nucleus acting on the inner portions of the dust torus is likely to play a critical role in controlling the accretion flow toward the nucleus and in forming the ionization cones seen in the narrow-line regions of Seyfert galaxies.