THE NATURE OF DAMPED Lyα SYSTEMS AND THEIR HOSTS IN THE STANDARD COLD DARK MATTER UNIVERSE

Abstract

Using adaptive mesh-refinement cosmological hydrodynamic simulations with a physically motivated supernova feedback prescription we show that the standard cold dark matter model can account for extant observed properties of damped Lyman alpha systems (DLAs). We then examine the properties of DLA host galaxies. We find: (1) While DLA hosts roughly trace the overall population of galaxies at all redshifts, they are always gas rich. (2) The history of DLA evolution reflects primarily the evolution of the underlying cosmic density, galaxy size and galaxy interactions. With higher density and more interactions at high redshift DLAs are larger in both absolute terms and in relative terms with respect to virial radii of halos. (3) The variety of DLAs at high redshift is richer with a large contribution coming from galactic filaments, created through close galaxy interactions. The portion of gaseous disks of galaxies where most stars reside makes relatively small contribution to DLA incidence at z=3-4. (4) The vast majority of DLAs arise in halos of mass M_h=10^10-10^12 Msun at z=1.6-4. At z=3-4, 20-30% of DLA hosts are Lyman Break Galaxies (LBGs). (5) Galactic winds play an indispensable role in shaping the kinematic properties of DLAs. Specifically, the high velocity width DLAs are a mixture of those arising in high mass, high velocity dispersion halos and those arising in smaller mass systems where cold gas clouds are entrained to high velocities by galactic winds. (6) In agreement with observations, we see a weak but noticeable evolution in DLA metallicity. The metallicity distribution centers at [Z/H]=-1.5 to -1 at z=3-4, with the peak moving to [Z/H]=-0.75 at z=1.6 and [Z/H]=-0.5 by z=0. (7) The star formation rate of DLA hosts is concentrated in the range 0.3-30Msun/yr at z=3-4, gradually shifting lower to peak at ~0.5-1 Msun/yr by z=0.