Published in "QSO Absorption Lines", Space Telescope Science Institute Symposium Series 2, 1987, eds. J. C. Blades, D. A. Turnshek and C. A. Norman
Abstract. QSO absorption systems with damped Ly-α lines belong to a distinct population of absorbers with properties that bring to mind the HI disks of spiral galaxies. A survey for damped Ly-α systems is described. It is shown that they occur more frequently along the line-of-sight than do normal spiral galaxies. The damped systems contribute a mass density per unit comoving volume that (a) dominates the baryon content of the universe at redshifts z = 2 - 3, and (b) is comparable to the mass per unit comoving volume contributed by luminous matter in present-day spiral galaxies. It is suggested that the damped absorbers are large HI disks which are the progenitors of normal spiral galaxies.
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