Unified model for quasar absorption line systems

We propose a three component model consisting of minihalos and galactic hal os with embedded thin discs for absorbers producing all the observed classe s of intervening quasar absorption line systems. We show that this model, b ased on CDM cosmology, can explain most of the observed statistical distrib utions of various types of absorption systems. Use of the Schechter luminos ity function for absorbers, on the other hand, is consistent with the obser vations only if the number of galaxies was larger in the past and reduced w ith time due to mergers. A strong chemical evolution in the halos of galaxi es is indicated by the observed properties of CIV lines. We discuss our res ults in the light of recent observations of the absorption line systems.