The Butcher-Oemler Effect in High Redshift X-ray Selected Clusters

Abstract

We are engaged in a wide-field, multi-colour imaging survey of X-ray selected clusters at intermediate and high redshift. We present blue fractions for the first 8 out of 29 clusters, covering almost a factor of 100 in X-ray luminosity. We find no correlation of blue fraction with redshift or X-ray luminosity. The lack of a correlation with L$_{X}$, places strong constraints on the importance of ram-pressure stripping as a driver of the Butcher-Oemler effect.Comment: 4 pages, 4 figures, to be puplished in the proceedings of the ''Sesto 2001-Tracing Cosmic Evolution with Galaxy Clusters'', Sesto 3-6 July 2001, Italy, eds, Stefano Borgan