The Evolution of Galaxies in Clusters at z~1 and Beyond

Prof Howard Yee (University of Toronto)

  Galaxy clusters provide a large range of environments for the study of
how environment affects galaxy evolution. I will present some recent
results on the evolution of galaxies in clusters at z~1 and beyond from two
large cluster surveys.  SpARCS is an imaging survey to look for galaxy clusters
up to z~2 using the cluster red-sequence technique based on a combination 
of Spitzer Space Telescopeˇ¦s IRAC 3.6um and ground-based zˇ¦-band images; GLASS 
is a multi-object spectroscopic survey of 10 of the richest SpARCS clusters 
at z~1 using the Gemini 8.2m telescopes. Analysis of GCLASS data show that 
galaxies in-falling into clusters at z~1 have their star formation quenched 
in a relatively short time scale of less than 500 Myr at an average location 
close to 0.5 r_200 (the cluster-centric radius within which the cluster is 
largely virialized). Combining the SpARCS and GCLASS data with Spitzer 
far-infrared 24um photometry as an indicator of star formation, we also 
find that lower mass in-falling galaxies appear to have episodes of enhanced 
star formation as they enter r_200 before the quenching of their star 
formation. Time permitting, I will also show some results on the growth 
of the BGCs (brightest cluster galaxies) at high redshifts and the 
evolution of the shape of galaxy clusters from z~2 to present.