Constraints on Galaxy Evolution and the Cosmological Constant From Damped Ly-alpha Absorbers

Abstract

We use the existing catalog of Damped Lyman-Alpha (DLA) systems to place constraints on the amount of evolution in the baryonic content of galaxies and on the value of the cosmological constant. The density of cold gas at redshifts z=3+-1 is obtained from the mean HI column density of DLAs per cosmological path length. This path length per unit redshift is in turn a sensitive function of the vacuum density parameter, Omega_v. We compare the total inferred mass of cold gas at high redshifts to that observed in stars today for flat cosmologies. We define "eta" to be net fraction of the baryonic content of local galaxies which was expelled since z=3, and use Bayesian inference to derive confidence regions in the (eta, Omega_v) plane. In all cosmologies we find that eta<0.4 with at least 95% confidence if <25% of the current stellar population formed before z=3. The most likely value of eta is negative, implying a net increase by several tens of percent in the baryonic mass of galaxies since z=3+-1. On the other hand, recent observations of high metal abundances in the intracluster medium of rich clusters (Loewenstein & Mushotzky 1996) require that metal-rich gas be expelled from galaxies in an amount approximately equal to the current mass in stars. Based on our results and the low metallicity observed in DLAs at z>2, we infer that more than half of the baryonic mass processed through galaxies must have been assembled and partly expelled from galaxies after z=2. We expect our constraints to improve considerably as the size of the DLA sample will increase with the forthcoming Sloan Digital Sky Survey.