Unification Issues and the AGN Torus

Abstract

Observations give strong support for the unification scheme of active galactic nuclei. Clumpiness of the toroidal obscuration is crucial for explaining the IR observations and has significance consequences for AGN classification: type 1 and type 2 viewing is an angle-dependent probability, not an absolute property. The broad line region (BLR) and the dusty torus are, respectively, the inner and outer segments, across the dust sublimation radius, of a continuous cloud distribution. Continuum X-ray obscuration comes mostly from the inner, BLR clouds. All clouds are embedded in a disk wind, whose mass outflow rate is diminishing as the accretion rate, i.e., AGN luminosity, is decreasing. The torus disappears when $L \la$ \E{42} erg/sec, the BLR at some lower, yet to be determined luminosities.