Assigned ID: 793 ----- Attempting Submission 1 (Fri Feb 25 23:42:35 GMT 2011) ----- Weak MgII absorbers are essential to understand galaxy environments because they trace the processes in the interface between galaxies and the intergalactic medium. These quasar absorption line systems, with a MgII 2796A rest frame equivalent width in the range 0.02 - 0.3 A, have been found to peak in abundance at a redshift of 1.2, and to dominate in number over the strong MgII absorbers that trace primarily low ionization regions in and around galaxies. The surprising thing is that the weak MgII absorbers, despite their locations typically 50-100kpc from luminous galaxies, have metallicities in many cases close to or exceeding the solar value, even at redshifts as high as 2. Our previous STIS archival survey of weak MgII absorbers in the present (redshifts 0 to 0.3) used the similar low ionization SiII(1260) and CII(1335) transitions as tracers, finding six absorbers along 25 sightlines. The COS archive now contains >100 quasar spectra which typically allow detection to more sensitive limits than our previous survey. Thus, we expect to find 25 weak MgII absorbers in the new survey to an equivalent width limit of 0.02A. In addition, we will probe the lower end of the equivalent width distribution to see if there is a turnover. We will now have a large enough sample of low redshift weak MgII absorbers to consider their hypothesized mixed origins in small (tens of parsecs), metal-rich pockets and in larger (kiloparsec scale), lower density clouds that have become less ionized at lower redshifts. This will allow us to explore volumes around galaxies that are populated by high velocity clouds, by satellite galaxies, and by gas ejected in galactic winds.

QUASAR ABSORPTION LINES AND IGM 12 Small false 0.0 0.0 false false false false SUPPORTED