Damped Lyα systems:: The progenitors of galaxy disks

I describe measurements of the kinematics of gas in damped Ly alpha systems which discriminate among competing theories for galaxy formation. Low-ion velocity profiles obtained with the HIRES echelle spectrograph of the Keck I telescope exhibit multi-component structures spanning velocity intervals Delta upsilon = (20,290) km s(-1). The velocity components exhibit "edge-leading" asymmetries in which the strongest component is at the edge of the profile. Other than rapidly rotating thick disks, all scenarios we tested with Monte Carlo techniques are inconsistent with the data. There are sufficient baryons in the metal-rich damped Ly alpha systems to explain the formation of the thick stellar disks seen in current spirals. We describe tests that can discriminate between rapidly rotating disks and the protogalactic clumps predicted by CDM models.