The star formation history of damped Lyman-alpha systems

The C II* technique for measuring star formation rates (SFRs) in damped Ly alpha systems (DLAs) is described. We measure cooling rates of the gas from the strength of C II* 1335.7 absorption lines, and infer heating rates by assuming the gas is heated by the grain photoelectric mechanism. Since the heating rates depend on the intensity of FUV radiation, we deduce the SFRS per unit area, which are comparable to the value in the Milky Way disk. From DLA statistics we obtain the SFBs per unit comoving volume at z = [1.6,4.5], which are similar to the rates in Lyman Break Galaxies. Implications such as the presence of a two-phase medium, metal production, and feedback processes are described. The model is tested and found to be consistent with observations.