Millions of Single Cloud Weak MgII Systems
Abstract
We report on a population of absorption systems selected by the presence of very weak Mg II doublets. A sub-population of these systems are iron enriched and have near solar metallicities. This would indicated advanced stages (i.e. few Gyr) of in situ star formation within the absorbing structures. From photoionization modeling, we infer low ionization fractions of f(HI/H)~0.01, and gas densities of ~0.1 cm-3. Since the maximum HI column densities are \~1017 cm-2, the inferred cloud sizes are ~10 pc. From their redshift number densities, this implies that their co-moving spatial density outnumbers normal bright galaxies by a factor of a few million.
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