Astronomy Tea Talk

Groups and clusters are important sites of galaxy evolution as well as interesting laboratories to study the interplay of galaxies, hot gas, and dark matter halos. A key challenge is to disentangle the roles that stellar mass and environmental processes play in shaping galaxy properties over time. To address this problem within a well-defined environment, we have constructed a sample of 129 galaxy groups in the COSMOS field. The groups are X-ray selected over the redshift range z=0-1 and have halo masses determined from stacked weak lensing. In this talk I will present results from two analyses of this group catalog. First, by measuring the lensing signal stacked around different candidate group centers (e.g. X-ray peak, brightest galaxy, centroid of member positions), we determine which observational tracer best identifies the center of mass of the halo. Second, we show how transformations in a galaxy's properties depend on its position within a group, and that changes in color and morphology take place over different timescales. I will also briefly discuss how a census of star-forming galaxies in these groups can aid in the interpretation of recent SZ measurements.