NARROW-BAND PHOTOMETRY AND THE EVOLUTION OF GALAXIES .3. THE INTERMEDIATE-REDSHIFT SAMPLE

A near-UV and blue rest frame narrow-band filter system is used to investigate the spectrophotometric evolution of elliptical galaxies. Data are presented for mean colors of ellipticals in six distant clusters (z = 0.37-0.46) for comparison with the present-day ellipticals and models of color evolution. We find good agreement with the UV-cold models of Guiderdoni & Rocca-Volmerangre, particularly with the confirmation of a strong post-MS light contribution at z = 0.4. The fraction of starforming to nonstarforming objects (Butcher-Oemler effect) is calculated from rest frame colors. Mean values of f(B) = 18% +/- 3% at z = 0.2 and 35% +/- 4% at z = 0.4 are found. Unlike near-blue colors, the 4000 angstrom break colors show little evolution, although this may be due to competing metallicity effects in post-MS light.