Friday, 29 February 2008

The color bimodality in galaxy clusters sinze z=0.9

Authors: Loh, Ellingson, Yee et al.

The red fraction as a function of redshift for galaxies with r/r200 < 0.25 (core), 0.25 <
r/r200 < 0.5, 0.5 < r/r200 < 1.0 and 1.0 < r/r200 < 2.0 (outskirts) and brighter than M⋆ + 1.5.

Galaxies in 1000 clusters from the Red Sequence Cluster Survey. They investigate the Butcher-Oemler effect in clusters and the radial dependence of it. They find that the evolution (incresing red fraction with decreasing redshift) is found at all radii, but strongest in the outskirts. The blue population in the outskirts might be an infalling population of galaxies, gradually tarnsforming into red galaxies. Not visible from the plot, but yet another conclusion: starburst type galaxies are less than 5% of all galaxies in the clusters, and therefore the galaxies making up the blue population are not likely to be a population of starbursting dwarfs.

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