"Encounters at the Edge of a Cluster: Environment's Effect on Galaxy Evolution"

ABSTRACT

While it is well-known that environment influences a galaxy's color, star-formation, and morphology, the exact mechanism is still unknown. For example, the fraction of S0 galaxies in clusters evolves strongly over cosmic time, and has been interpreted as the conversion of spirals into S0s in the cores of clusters. However, I will present evidence that the formation of S0s occurs outside massive clusters, in less dense environments. First, we find that lower-mass systems are responsible for the evolving S0 fraction. Second, we find no signs of recent or ongoing star-formation in the S0s of SG1120, a z~0.4 system of four gravitationally-bound groups that will coalesce into a massive cluster by z=0, placing S0 formation even father from the cluster core. Finally, I will highlight a unique spectroscopic survey capable of isolating the infall regions of ~20 clusters from 0.4<z<0.8, enabling us to directly explore the environment where the transformation is taking place.