A simple analytical model for estimating the fraction (Ωgas) of matter in gaseous form within the collapsed dark matter (DM) haloes is presented. The model is developed using (i) the Press-Schechter formalism to estimate the fraction of baryons in DM haloes, and (ii) the observational estimates of the star formation rate at different redshifts. The prediction for Ωgas from the model is in broad agreement with the observed abundance of the damped Lyα systems. Furthermore, it can be used for estimating the circular velocities of the collapsed haloes at different redshifts, which could be compared with future observations.
