Studying the Gaseous Phases of Galaxies with Background QSOs

High resolution rest frame UV quasar absorption spectra covering low and high ionization species, as well as the Lyman series lines, provide remarkably detailed information about the gaseous phases of galaxies and their environments. For redshifts less than 1.5, many important chemical transitions remain in the observed ultraviolet wavelength range. I present examples of absorption that arises from lines of sight through a variety of structures, drawn from UV spectra recently obtained with STIS/HST. Even with the greater sensitivity of COS/HST there will be a limit to how many systems can be studied in detail. However, there is a great variety in the morphology of the phases of gas that we observe, even passing through different regions of the same galaxy. In order to compile a fair sample of the gaseous structures present during every epoch of cosmic history, hundreds of systems must be sampled. Multiple lines of sight through the same structures are needed, as well as some probing nearby structures whose luminous hosts have been studied with more standard techniques. Combined with high resolution optical and near--IR ground--based spectra, it will be possible to uniformly study the gaseous morphologies of galaxies of all types through their entire evolutionary histories.