Abstract
The galaxy distribution in six Butcher-Oemler clusters is analyzed in order to obtain separate core radii for the blue galaxies and for the red E-sequence galaxies. By fitting these distributions with isothermal spheres via maximum-likelihood techniques, the core radius for the blue galaxies is shown to be nearly three times that of the red galaxies. While the general trend of the blue/red galaxy segregation was noticed by Butcher and Oemler, the analysis is presented here places this result on firm statistical ground. A test for luminosity segregation gives only marginally significant results, while a comparison of differential luminosity functions shows that blue galaxies, in their quiescent state, are likely to be about 1 mag fainter than red E-sequence galaxies. When combined with each other, the two previous results imply that mass segregation cannot explain the broad blue galaxy distribution. A discussion of dynamical considerations particularly the relative velocity dispersions of blue and red galaxies - is included to show how the blue/red galaxy segregation might arise.
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