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The 2dF Galaxy Redshift Survey: The blue galaxy fraction and implications for the Butcher-Oemler effect

Roberto De Propris, Matthew Colless, John Peacock, Warrick Couch, Simon Driver, Michael Balogh, Ivan Baldry, Carlton Baugh, Joss Bland-Hawthorn, Terry Bridges, Russell Cannon, Shaun Cole, Chris Collins, Nicholas Cross, Gavin Dalton, George Efstathiou, Richard Ellis, Carlos Frenk, Karl Glazebrook, Edward Hawkins, Carole Jackson, Ofer Lahav, Ian Lewis, Stuart Lumsden, Steve Maddox, Darren Madgwick, Peder Norberg, Will Percival, Bruce Peterson, Will Sutherland, Keith Taylor

astro-pharXiv:astro-ph/0402652

Abstract

We derive the fraction of blue galaxies in a sample of clusters at z < 0.11 and the general field at the same redshift. The value of the blue fraction is observed to depend on the luminosity limit adopted, cluster-centric radius and, more generally, local galaxy density, but it does not depend on cluster properties. Changes in the blue fraction are due to variations in the relative proportions of red and blue galaxies but the star formation rate for these two galaxy groups remains unchanged. Our results are most consistent with a model where the star formation rate declines rapidly and the blue galaxies tend to be dwarfs and do not favour mechanisms where the Butcher-Oemler effect is caused by processes specific to the cluster environment.

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