STAR FORMATION AND UV COLORS OF THE BRIGHTEST CLUSTER GALAXIES IN THE REPRESENTATIVE<i>XMM-NEWTON</i>CLUSTER STRUCTURE SURVEY

Abstract

We present UV broadband photometry and optical emission-line measurements for\na sample of 32 Brightest Cluster Galaxies (BCGs) in clusters of the\nRepresentative XMM-Newton Cluster Structure Survey (REXCESS) with z =\n0.06-0.18. The REXCESS clusters, chosen to study scaling relations in clusters\nof galaxies, have X-ray measurements of high quality. The trends of star\nformation and BCG colors with BCG and host properties can be investigated with\nthis sample. The UV photometry comes from the XMM Optical Monitor, supplemented\nby existing archival GALEX photometry. We detected H\\alpha and forbidden line\nemission in 7 (22%) of these BCGs, in optical spectra. All of the emission-line\nBCGs occupy clusters classified as cool cores, for an emission-line incidence\nrate of 70% for BCGs in cool core clusters. Significant correlations between\nthe H\\alpha equivalent widths, excess UV production in the BCG, and the\npresence of dense, X-ray bright intracluster gas with a short cooling time are\nseen, including the fact that all of the H\\alpha emitters inhabit systems with\nshort central cooling times and high central ICM densities. Estimates of the\nstar formation rates based on H\\alpha and UV excesses are consistent with each\nother in these 7 systems, ranging from 0.1-8 solar masses per year. The\nincidence of emission-line BCGs in the REXCESS sample is intermediate, somewhat\nlower than in other X-ray selected samples (-35%), and somewhat higher than but\nstatistically consistent with optically selected, slightly lower redshift BCG\nsamples (-10-15%). The UV-optical colors (UVW1-R-4.7\\pm0.3) of REXCESS BCGs\nwithout strong optical emission lines are consistent with those predicted from\ntemplates and observations of ellipticals dominated by old stellar populations.\nWe see no trend in UV-optical colors with optical luminosity, R-K color, X-ray\ntemperature, redshift, or offset between X-ray centroid and X-ray peak (&lt;w&gt;).\n