Damped Lyα absorber and the faint end of the galaxy luminosity function at high redshift

We combine predictions for several hierarchical cosmogonies with observational evidence on damped Ly alpha systems (DLASs) to establish a correspondence between the high-redshift galaxy population and the properties of DLASs. We assume that high-redshift galaxies and damped Ly alpha systems are hosted by the same dark matter halos and require consistency between the predicted halo space density, the rate of incidence and the velocity width distribution of damped Ly alpha systems, and the observed galaxy luminosity function at the bright end. We arrive at the following results: (1) predicted impact parameters between the damped absorption system and the luminous parts of the absorbing galaxy are expected to be very small (0 .3-1 ) for most galaxies; (2) luminosities of galaxies causing damped absorption are generally fainter than m(R) = 25, and damped Ly alpha systems are predicted to sample preferentially the outer regions of galaxies at the faint end of the galaxy luminosity function at high redshift. Therefore, DLASs should currently provide the best probe of the progenitors of normal present-day galaxies.