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

We combine predictions for several hierarchical cosmogonies with observatio nal evidence on damped Ly alpha systems (DLASs) to establish a corresponden ce between the high-redshift galaxy population and the properties of DLASs. We assume that high-redshift galaxies and damped Ly alpha systems are host ed by the same dark matter halos and require consistency between the predic ted halo space density, the rate of incidence and the velocity width distri bution of damped Ly alpha systems, and the observed galaxy luminosity funct ion at the bright end. We arrive at the following results: (1) predicted im pact 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 gener ally fainter than m(R) = 25, and damped Ly alpha systems are predicted to s ample preferentially the outer regions of galaxies at the faint end of the galaxy luminosity function at high redshift. Therefore, DLASs should curren tly provide the best probe of the progenitors of normal present-day galaxie s.