Journal Article

An environmental Butcher–Oemler effect in intermediate-redshift X-ray clusters*

S. A. Urquhart, J. P. Willis, H. Hoekstra and M. Pierre

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 406, issue 1, pages 368-381
Published in print July 2010 | ISSN: 0035-8711
Published online July 2010 | e-ISSN: 1365-2966 | DOI:
An environmental Butcher–Oemler effect in intermediate-redshift X-ray clusters*

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We present uniform Canada–France–Hawaii Telescope (CFHT) Megacam g and r photometry for 34 X-ray-selected galaxy clusters drawn from the X-ray Multi-Mirror (XMM) Large Scale Structure (LSS) survey and the Canadian Cluster Comparison Project (CCCP). The clusters possess well-determined X-ray temperatures spanning the range 1 < kT(keV) < 12. In addition, the clusters occupy a relatively narrow redshift interval (0.15 < z < 0.41) in order to minimize any redshift-dependent photometric effects. We investigate the colour bimodality of the cluster galaxy populations and compute blue fractions using criteria derived by Butcher & Oemler. We identify a trend to observe increasing blue fraction versus redshift in common with numerous previous studies of cluster galaxy populations. However, in addition we identify an environmental dependence of cluster blue fraction in that cool (low-mass) clusters display higher blue fractions than hotter (higher mass) clusters. Finally, we tentatively identify a small excess population of extremely blue galaxies in the coolest X-ray clusters (essentially massive groups) and note that these may be the signature of actively starbursting galaxies driven by galaxy–galaxy interactions in the group environment.

Keywords: galaxies: clusters: general

Journal Article.  8506 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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