Rutgers University Astrophysics Seminar

Abstract: I will discuss how galaxies are transformed by ram pressure stripping and gravitational encounters in the environment of the Virgo Cluster, the nearest cluster of galaxies. This work is based on optical, H-alpha, HI, Radio Continuum, GALEX, and Spitzer data for a large sample of spiral and peculiar galaxies in Virgo. There is widespread evidence that most cluster spirals are strongly affected by ram pressure stripping of the gas in a galaxy's interstellar medium by an interaction with the gas in the intracluster medium. Many galaxies show evidence for ongoing stripping, including ridges of polarized radio continuum emission on the leading edge and HI tails on the trailing side. From stellar population studies and comparisons of observations with simulations, we can identify galaxies in different stages of stripping. Many galaxies which were stripped in the past have truncated and symmetric gas disks but normal stellar disks, and have properties intermediate between spiral and S0 galaxies. I will show Hubble Space Telescope ACS images of NGC 4522, one of the nearest and clearest cases for ongoing ram pressure stripping. The images show extraplanar star clusters which formed from stripped gas, large-scale dust lanes leaving the plane of the stellar disk, and small-scale head-tail dust features, which we propose are dense gas clouds being ablated by the ICM wind after the low density ISM has been stripped. Finally, I will show that many galaxies are also strongly affected by gravitational encounters, including low and high-velocity interactions and merging.