Monday, March 12, 2012
Cahill, Hameetman Auditorium
Astronomy Tea Talk
Galaxies in X-ray Groups: Finding Halo Centers and Tracking Evolution
Matt George, UC Berkeley
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.