Spectral energy distributions for galaxies in high redshift clusters - I. Methods and application to three clusters with 0.22 z 0.31

Using CCDs and a range of intermediate band filters we have imaged three moderate redshift (0.22 ≼ z ≼ 0.31) clusters and derived low-resolution spectral energy distributions for about 50 galaxies per cluster to a limit of $$R_f\sim21$$. The average flux distributions are in good agreement with those expected from published K-corrections and local knowledge of the colour–luminosity relation for early-type galaxies; the brightest members do not appear to be anomalous. Some blue galaxies are found: their average spectral energy distribution approximates to an Sbc galaxy at the cluster redshift. At the longest wavelength studied (860 nm) some galaxies are significantly redder than the cluster average; the nature of these objects remains unclear but they do appear to be cluster members. The important question of whether there is any evolution in the early-type population depends sensitively on corrections made for foreground reddening and for the colour–luminosity relations. With some uncertainties there is room for a small amount of evolution consistent with previous estimates. At higher redshifts where evolutionary effects are expected to be larger the technique will be a powerful way to study large galaxy samples at known epochs.