Publications of the MPIfR
Optical & Infrared
Interferometry Group
Vollmer, B., Beckert, T., Duschl, W.J.
From the Circumnuclear Disk in the Galactic
Center to thick, obscuring tori of AGNs
Astronomy and Astrophysics, v.413, p.949-957 (2004)
Abstract
We compare three different models of clumpy gas disk and show that the
Circumnuclear Disk (CND) in the Galactic Center and a putative,
geometrically thick, obscuring torus are best explained by a
collisional
model consisting of quasi-stable, self-gravitating clouds. Kinetic
energy of clouds is gained by mass inflow and dissipated in cloud
collisions. The collisions give rise to a viscosity in a spatially
averaged gas dynamical picture, which connects them to angular momentum
transport and mass inflow. It is found that CND and torus share the
same
gas physics in our description, where the mass of clouds is 20-50
M_⊙ and their density is close to the limit of disruption by tidal
shear. We show that the difference between a transparent CND and an
obscuring torus is the gas mass and the velocity dispersion of the
clouds. A change in gas supply and the dissipation of kinetic energy
can
turn a torus into a CND-like structure and vice versa. Any massive
torus
will naturally lead to sufficiently high mass accretion rates to feed a
luminous AGN. For a geometrically thick torus to obscure the view to
the
center even super-Eddington accretions rates with respect to the
central
black hole are required.
You can get this publication ...