Joint Astrophysics Colloquium

Galaxy Clusters at 0 < z < 2 in the IRAC Shallow Cluster Survey

Mark Brodwin

NOAO

Using a probabilistic photometric redshift-based approach combining Spitzer mid-IR and NOAO optical data, we have discovered 335 new galaxy clusters and groups in the NDWFS Bootes field, over 100 of which are at 1 < z < 2. To date we have spectroscopically confirmed 10 of these high redshift clusters, spanning 1.06 < z < 1.41. Deep follow-up Spitzer and HST data, currently being obtained for 18 of the z > 1 clusters, allows detailed studies of the mass assembly and star formation histories in massive galaxies at this key epoch. In this regime massive cluster galaxies have the mean colors predicted by simple passive evolution models with high (z > 3) formation redshifts. They also show strong evidence of morphological evolution, with the fraction of mergers and disturbed morphologies increasing with lookback time. Finally we have measured strong clustering in the galaxy cluster population at 0.25 < z < 1.5, from which we infer that the cluster sample has an average mass of nearly 10¹⁴ M_sun.