Ram Pressure Stripping in Groups: Comparing Theory and Observations

Ram pressure stripping may be one of the dominant mechanisms driving the evolution of galaxies in groups and clusters. In this paper, models of ram pressure stripping are confronted with observations of galaxy colors and star formation rates using a group catalog drawn from the Sloan Digital Sky Survey and model predictions based on an analytical model of stripping presented in Hester (2006). An observed increase in the fraction of galaxies residing on the red sequence, the red fraction, with both increasing group mass, Mgr, and decreasing satellite luminosity, Lsat, can be understood using the model. The size of the change in the red fraction with changing Mgr or Lsat can be understood in terms of the effect of the scatter in satellite and cluster morphologies and satellite orbits on the relationship between Mgr and Lsat and the stripped gas fraction. Observations of the group galaxies’ Hδ and 4000Å break spectral measures and a comparison of the distribution of SFR/M∗ for star forming galaxies in the groups and in isolation both indicate that the color differences observed in the groups are the result of slowly declining SFRs, as expected if the color change is driven by stripping of the outer H i disk. Subject headings: galaxies: evolution — galaxies:clusters:general