KINEMATIC PROPERTIES OF DAMPED LYMAN ALPHA SYSTEMS

Abstract

In a previous paper, we determined the statistical distributions for various classes of QSO absorption systems in the framework of the CDM model of the universe with a mass distribution of dark matter halos as given by the Press Schechter mechanism. These were shown to be consistent with the observed distributions for reasonable choices of model parameters. In this paper, we generate Voigt profiles of C IV lines associated with Damped Lyman Alpha systems in the framework of this model, taking into account rotation of disks and random motion of clouds embedded in galactic halos. We compare these with the profiles for a sample of 32 Damped Lyman Alpha systems collected from the literature by performing several statistical tests. These tests compare the width and the degree of asymmetry in the line profiles produced by the rotation of randomly inclined disks and the random velocity of clouds in the galactic halos, with the corresponding quantities in the observed profiles. We find that the kinematic properties predicted by the model are in good agreement with observations provided the disk thickness is about ten thousand times smaller than its radius, which indicates that the material in the disks is concentrated in dense clouds with roughly unit covering factor.