  Damped Lyman-alpha systems (DLAs) are useful probes of star formation and
galaxy formation at high redshift. We study the physical properties of DLAs and
their relationship to Lyman-break galaxies using cosmological hydrodynamic
simulations based on the concordance Lambda cold dark matter model. Fundamental
statistics such as global neutral hydrogen (HI) mass density, HI column density
distribution function, DLA rate-of-incidence and mean halo mass of DLAs are
reproduced reasonably well by the simulations, but with some deviations that
need to be understood better in the future. We discuss the feedback effects by
supernovae and galactic winds on the DLA distribution. We also compute the
[C_II] emission from neutral gas in high-z galaxies, and make predictions for
the future observations by ALMA and SPICA. Agreement and disagreement between
simulations and observations are discussed, as well as the future directions of
our DLA research.

Astrophysics