The Star Formation History of Damped Lyα Absorbers

The local power law relationship between the surface densities of neutralhydrogen gas and star formation rate (SFR) can be used to explore the SFRproperties of damped Lyman alpha (DLA) systems at higher redshift. We find thatwhile the SFR densities for DLA systems are consistent with luminous starforming galaxies at redshifts below z~0.6, at higher redshifts their SFRdensity is too low for them to provide a significant contribution to the cosmicstar formation history (SFH). This suggests that the majority of DLAs may be adistinct population from the Lyman break galaxies (LBGs) or submillimeterstar-forming galaxies that together dominate the SFR density at high redshift.It is also possible that the DLAs do not trace the bulk of the neutral gas athigh redshift. The metallicity properties of DLAs are consistent with thisinterpretation. The DLAs show a metal mass density lower by two orders ofmagnitude at all redshifts than that inferred from the SFH of the universe.These results are consistent with DLAs being dominated by low mass systemshaving low SFRs or a late onset of star formation, similar to the starformation histories of dwarf galaxies in the local universe.Comment: 9 pages, 5 figures, accepted for publication in Ap