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Paper: Color Bimodality in Galaxy Clusters since z ~ 0.9
Volume: 379, Cosmic Frontiers
Page: 294
Authors: Ellingson, E.; Loh, Y.S.; Yee, H.K.C.; Gilbank, D.G.; Gladders, M.D.; Barrientos, F.
Abstract: We analyze galaxy colors from a sample of ~ 2000 galaxy clusters with 0.4 < z < 0.9 and richness greater than Bgc= 300 Mpc1.77 (~ 450 km/sec) from the 90 square degree RCS-1 survey. We find that cluster galaxies exhibit bimodality, with a distinct red sequence plus a broader population of blue galaxies, (e.g., Hogg et al. 2003). This latter component increases with redshift and radius, confirming a version of the ‘Butcher-Oemler’ effect (Butcher & Oemler 1978, and many others subsequently). There may be a mild differential evolution as a function of cluster radius. The properties of the blue galaxies are predominantly those of normal star-forming spirals, with only a small fraction showing the very blue colors expected of unobscured starburst galaxies. We suggest that the bulk of these galaxies are normal infalling field galaxies which will join the cluster red sequence as their star formation declines.
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