Cii* Absorption in Damped Lyα Systems. II. A New Window on the Star Formation History of the Universe

Starting from the SFR per unit physical area, determined for DLAs using the CII* method, we obtain the SFR per unit comoving volume at $z$ $\approx$ 3, andfind that it agrees with that for the Lyman Break Galaxies (LBGs). Though themass of produced stars indicated by the SFRs is consistent with the currentdensities of known stellar populations, the mass of metals produced by $z$=2.5is 30 times larger than detected in absorption in DLAs. The most likelysolutions to this ``missing metals'' problem is that star formation occurs incompact bulge regions. We search for evidence of feedback and find nocorrelations between the SFR per unit area and N(H I), but possiblecorrelations between SFR per unit area and low-ion velocity width and SFR perunit area and metal abundance. We show that (a) the correlation between coolingrate and dust-to-gas ratio is positive evidence for grain photoelectricheating, (b) the CMB does not significantly populate the C II excitedfine-structure states, and (c) the ratio of CII* to resonance-line opticaldepths is a sensitive probe of the multi-phase structure of the DLA gas. Weaddress recent arguments that DLAs are comprised only of WNM gas, and show themto be inconclusive. Despite the rough agreement between SFR per unit comovingvolume for DLAs and LBGs, current evidence indicates these are distinctpopulations