In order to investigate the origin of the far-UV ( FUV ) flux from the early-type galaxies , Galaxy Evolution Explorer ( GALEX ) is collecting the UV data for the elliptical-rich clusters at moderate redshifts ( z < 0.2 ) where the dominant FUV source is predicted to be hot horizontal-branch ( HB ) stars and their post-HB progeny .
Here we present our first result for the early-type galaxies in Abell 2670 at z = 0.076 .
Compared to NGC 1399 , a nearby giant elliptical galaxy in the Fornax cluster , it appears that the rest-frame FUV - V color of the giant ellipticals gets redder by \sim 0.7 mag at the distance of Abell 2670 ( z = 0.076 ; look-back time \approx 1.0 Gyr ) .
Although a detailed comparison with the models is postponed until more cluster data are accumulated , it is interesting to note that this value is consistent with the variation predicted by the population synthesis models where the mean temperature of HB stars declines rapidly with increasing look-back time .