The dynamical state of a thick cloudy torus around an AGN

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: tbeckert@mpifr-bonn.mpg.de
² Institut für Theoretische Astrophysik der Universität Heidelberg, Tiergartenstraße 15, 69121 Heidelberg, Germany

Received: 25 February 2004
Accepted: 6 July 2004

Abstract

We present stationary models of obscuring dusty tori around active galactic nuclei. Vertical and radial structure are discussed separately based on a dynamical approach to a cloudy accretion flow. The vertical cloud distribution is described by a modified isothermal disk for arbitrary thickness of the torus with a wide funnel along the symmetry axis. The radial accretion flow is a consequence of cloud–cloud collisions. Accretion in the combined gravitational potential of central black hole and stellar cluster generates free energy, which is dissipated in collisions, and maintains the thickness of the torus. We focus on the largest clouds at the tidal shear limit, which will dominate the dynamics and the appearance of torus. Successful obscuration as required by unified schemes of AGN is achieved for large mass accretion rates above the Eddington limit of the central black hole. A complete quantitative treatment for the putative torus in the prototypical Seyfert 2 nucleus of NGC 1068 is given.