The Look‐back Time Evolution of Far‐Ultraviolet Flux from the Brightest Cluster Elliptical Galaxies at z < 0.2

We present the GALEX UV photometry of the elliptical galaxies in Abellclusters at moderate redshifts (z < 0.2) for the study of the look-back timeevolution of the UV upturn phenomenon. The brightest elliptical galaxies (M_r <-22) in 12 remote clusters are compared with the nearby giant ellipticalgalaxies of comparable optical luminosity in the Fornax and Virgo clusters. Thesample galaxies presented here appear to be quiescent without signs of massivestar formation or strong nuclear activity, and show smooth, extended profilesin their UV images indicating that the far-UV (FUV) light is mostly produced byhot stars in the underlying old stellar population. Compared to theircounterparts in nearby clusters, the FUV flux of cluster giant ellipticalgalaxies at moderate redshifts fades rapidly with ~ 2 Gyrs of look-back time,and the observed pace in FUV - V color evolution agrees reasonably well withthe prediction from the population synthesis models where the dominant FUVsource is hot horizontal-branch stars and their progeny. A similar amount ofcolor spread (~ 1 mag) in FUV - V exists among the brightest cluster ellipticalgalaxies at z ~ 0.1, as observed among the nearby giant elliptical galaxies ofcomparable optical luminosity.Comment: Accepted for publication in the Special GALEX ApJ Supplement, December 200