Schedule Mar 18, 2011
The Era of Star Formation in High-Redshift Galaxy Clusters in the IRAC Shallow Cluster Survey (ISCS)
Mark Brodwin (Harvard, CfA)

The Spitzer/IRAC Shallow Cluster Survey (ISCS) is a stellar mass-selected sample of 335 galaxy clusters and groups spanning 0 < z < 2. Of the ~100 clusters at z>1, 20 have been spectroscopically confirmed to date, out to a redshift of z=1.5. The ISCS clusters are selected independently of the red-sequence, using a probabilistic photometric redshift method, and therefore offer an unbiased view of the early formation and evolution of the richest environments in the Universe. Using multi-wavelength follow-up observations from the X-ray to the millimeter, and in particular, deep 24um imaging from Spitzer, we have measured the instantaneous star formation rate in 18 spectroscopically confirmed clusters at 1 < z < 1.5. The high specific star formation rates observed in these cluster galaxies are similar to or greater than that in field galaxies in this redshift range. Unlike in nearby clusters, the star formation rate rises dramatically with decreasing radius, roughly tracing the stellar mass. At the highest redshifts, z >~ 1.4, the specific star formation rate is nearly independent of cluster radius, indicating that we are finally probing the era where quenching has not yet shut off star formation in galaxy clusters.

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