Dr. Alan Dressler, Carnegie Observatories, Pasadena, Calif
“Infalling groups and galaxy evolution in the IMACS Cluster Building Survey”
Abstract
From a photometric/spectroscopic study of z~0.4 clusters and field galaxies, using the wide field of the IMACS instrument on the Magellan-Baade telescope, we have studied infalling galaxies that have built typical rich clusters, and compared them to field galaxies over the full range of galaxy environment. The results emphasize the important role of infalling groups of galaxies in building a cluster, and evidence that significant quenching of starforming galaxies occurs in such groups --- in clusters and the field -- outside the cluster environment. Our study also suggests a new interpretation of the role that starbursts play in the evolution of galaxies at this epoch.