Damped Lyman α systems } have much higher column densities in absorption, so that the H I resonance line is in a different part of the curve of growth. These are taken to be genuine disk galaxies, and extensive surveys (for example Wolfe et al 1986 ApJSupp 61, 249) have been carried out in hopes of watching spiral disks evolve. Straightforward assumptions indicate that these contain most of the neutral gas in teh Universe for a wide range of redshift. Metal lines are
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This note was uploaded on 11/10/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.