The Nature of Damped Lyman Alpha Systems and Their Hosts in the Standard
  Cold Dark Matter Universe
  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.
