Constraints on Models of Galaxy Formation from the Evolution of Damped Ly$\alpha$ Absorption Systems

Abstract

There is accumulating observational evidence suggesting that damped Ly$\alpha$ absorption systems systems are the progenitors of present-day spiral galaxies. We use the observed properties of these systems to place constraints on the history of star formation in galactic disks, and on cosmological theories of structure formation in the universe. We show that the observed increase in $\Omega_{HI}$ contributed by damped Ly$\alpha$ systems at high redshift implies that star formation must have been considerably less efficient in the past. We also show that the data can constrain cosmological models in which structure forms at late epochs. A mixed dark matter (MDM) model with $\Omega_{\nu}=0.3$ is unable to reproduce the mass densities of cold gas seen at high redshift, even in the absence of any star formation. We show that at redshifts greater than 3, this model predicts that the total baryonic mass contained in dark matter halos with circular velocities $V_c > 35$ km s$^{-1}$ is less than the observed mass of HI in damped systems. At these redshifts, the photo-ionizing background would prevent gas from dissipating and collapsing to form high column density systems in halos smaller than 35 km s$^{-1}$. MDM models are thus ruled out by the observations.