Unified model for quasar absorption line systems

We propose a three component model consisting of minihalos and galactic halos with embedded thin discs for absorbers producing all the observed classes of intervening quasar absorption line systems. We show that this model, based on CDM cosmology, can explain most of the observed statistical distributions of various types of absorption systems. Use of the Schechter luminosity function for absorbers, on the other hand, is consistent with the observations only if the number of galaxies was larger in the past and reduced with time due to mergers. A strong chemical evolution in the halos of galaxies is indicated by the observed properties of CIV lines. We discuss our results in the light of the recent observations of the absorption line systems.