Program: GS-2013A-Q-85

Unlike low (z~0) and high (z~1) redshift samples, intermediate redshift groups are found in a wide range of dynamical states. This mixture of virialized and dynamically unevolved groups is the ideal sample with which to study SF quenching mechanisms, including those that require an evolved group halo (e.g. ram-pressure stripping) and those that function on smaller subhalo scales (e.g. tidal interactions and mergers). By looking at the infall regions of intermediate-z galaxy groups, we can study the elusive environmental mechanism(s) transforming galaxy properties. Preliminary analysis of the fraction of red galaxies as a function of radius in the Group Environment and Evolution Collaboration (GEEC) group catalog suggests that X-ray faint groups have a steeper fred trend with radius than X-ray bright groups, and that the difference is strongest at large radii. This preliminary result hints at different underlying transformation mechanisms in X-ray bright and faint groups. To better understand the processes driving the environmental quenching of galaxies, we propose a programme to obtain spectra for >200 new members of 15 GEEC groups (8 X-ray bright and 7 X-ray faint) resulting in high spectroscopic completeness to large radii. We will study galaxy properties as a function of stellar mass and group-centric radius, and determine the dependence of these trends on the properties of the host environment including halo mass, dynamical state and X-ray luminosity.