Galaxy Evolution from QSO Absorption--Selected Samples

Abstract

We present results of surveys for high redshift field galaxies selected by their having produced detectable absorption in the spectra of background QSOs. Such surveys, in essence selected by gas cross-section rather than by flux density, are almost completely independent of the conventional magnitude--limited redshift survey, and allow one to follow objects of normal luminosity well beyond $z\sim 1$, the redshift at which many of the standard techniques break down. We summarize the principal results for our completed survey at $z \le 1$, and give the preliminary results of a second survey designed to extend the sample to $z=1.6$. A general conclusion is that normal field galaxies exhibit strikingly little evolution in their space density, luminosity, and optical/IR colors to redshifts as high as $z\sim 1.5$. We discuss both the techniques involved and the implications of the results.