Flared dust disks and the IR emission of AGN

We describe an accelerated version of the two-dimensional (2D) ray-tracing code for radiative transfer in disk configurations developed by Men'shchikov & Henning (1997). This new code enabled us to perform an extensive scan of the parameter space of flared dust disks around active galactic nuclei (AGN). Among the parameters influencing spectral energy distributions, we varied the dust model, the density distribution, the opening angle, and the optical depth of the disks as well as the anisotropy of the radiation field of the central source. Our aim was to find configurations that produce continuum spectra similar to the observed ones which show no 10 mu m emission feature along lines of sight where the central source is not obscured. We found that optically thick disks in combination with a strong anisotropic 7 radiation source can produce such spectral energy distributions. The best-fit models show a very high optical depth of tau(200nm) approximate to 1000 (along the equatorial plane), an opening angle of 90 degrees, and a density distribution proportional to r(-1). As the strong anisotropy of the source radiation prevents significant silicate emission features from appearing, we see no need for the depletion of silicate grains by shocks or for the presence of compact cores.