Radiation fields in moving media: effects of many spectral lines in AGN accretion disks

Abstract

Analytical solutions of the radiative transfer equation recently derived for differentially moving media allow the efficient inclusion of an arbitrarily large number of spectral lines both in a deterministic and in a stochastic way. For a deterministic line set and not too small velocities, a high computational speed-up is achieved if the solution is expressed not in terms of the extinction coefficient but by its much smoother wavelength integral. The assumption of a Poisson point process for the number of lines, combined with suitable distributions for the line positions and other line parameters, is a flexible presentation of the wavelength dependence of the line extinction coefficient which well describes deterministic “real” lines and requires only few parameters. The intricate connection between line properties and the emergent intensity can then be evaluated to a large part analytically. Assuming Lorentz profiles and a power law for the line strength distribution, we discuss the effect of many spectral lines on the radiation field of a typical AGN accretion disk, in particular, on the emerging radiation and on its diffusion limit holding in the interior.