Background

Abstract

This report provides an overview of research into high redshift galaxies and galaxy evolution from an ob servational perspective over the period 1990 to 1993. Only references to the literature from this period are given in order to provide a snapshot of current research. Several related topics (e.g. high-redshift galaxies as probes of cosmological models, galaxy interactions and evolution at low redshift, and gravitational lensing) are dealt with elsewhere in this volume. clusters. A second sizable catalogue of high-redshift clusters appeared 25 , while several groups investigated the high fraction of blue galaxies in distant clusters (the Butcher-Oemler effect), both through photometric studies 87 and spectroscopically 36,37 . These studies confirmed the strong increase in the blue fraction with redshift and demonstrated that it is largely composed of emission-line and E+A galaxies that are much scarcer in clusters selection biases with the in rich to the all have a large blue fraction at high redshift, with the richer groups redder at low redshift. is also 36,2 for of the in with z=0.5-l, with as as present-day ellipticals by zssl. Ly a absorbers have been discovered through their Ly a, [Oil], H/J or CO , and appear consistent with large star-forming disks. Recent observations suggest that the clustering of Ly a-emitting galaxies around Ly a absorbers, and of the absorbers themselves, is strong over scales of several Mpc, in contrast to the weak clustering of faint galaxies 108,48 the limit (LL) and metal line (Mgll and CIV) absorbers on scales decrease the of (clouds) at larger impact equivalent width of the Mgll systems decreases with time , implying a decrease in the the number of clouds per . The Mgll and CIV systems are also clustered 84,100 on scales of several Mpc. QSO of dark in