Gas and star formation in galaxies and QSO absorption line systems

The statistical properties of damped Lyα systems (DLAs) and the H i disks in local galaxies are in very good agreement. We infer from this that DLAs arise in normal spiral galaxies. DLAs contain most of the neutral gas in the Universe and, as such, provide the reservoir of fuel for star formation. However, molecular detections in DLAs are rare and the implied star formation rate density from DLAs is much lower than the value measured from emission lines. In this talk I argue that the molecules do exist in DLA galaxies, but are locked up in small regions not necessarily cospatial with the high column density H i. If the molecules are taken into account, DLA galaxies can probably account for most of the star formation rate density at high z.