Do accretion disk instabilities drive a thermal wind in AGN?

Abstract

A linear stability analysis of a warped accretion disk beyond the Bardeen‐Petterson radius has shown that this is violently unstable to shearing instabilities of a size comparable with the disk density scale height. We hypothesize that this instability will lead to fragmentation of the disk in the unstable zone, even in objects which have only a moderate misalignment between the angular momentum vectors of the outer accretion disk and the central black hole. Compton heating and evaporation of the clouds resulting from disk fragmentation is shown to be capable of driving a thermal Parker wind in these cases, which, if optically thick to electron scattering will result in an electron scattering photosphere. We propose that this is the source of the ‘‘big blue bump’’ UV emission seen in QSOs and other AGN. In such a model the broad‐line region is caused by photoionization by this UV field of both the outer accretion disk and of cloud fragments entrained in the wind. We suggest that such a model is capable of...