Alan Dressler, OCIW

Morphological and Spectroscopic Evolution of Galaxies in Rich Clusters
since z ~ 0.5

In the larger context of studies of galaxy evolution with significant 
lookback times, the marked changes in the stellar populations and 
morphological types of galaxies in clusters offers a special opportunity
to investigate the role of environment.  The `MORPHS' group has been
conducting a ground-based spectroscopic survey and HST-imaging
program of 10 clusters of galaxies at redshifts z ~ 0.5.  The study
provides evidence that most cluster elliptical galaxies are old while 
most S0 galaxies are not, and that the many starforming galaxies in
such intermediate-redshift clusters have experienced episodic star
formation whose cause, and evolutionary history, is not well understood.