Spectral energy distributions for galaxies in high-redshift clusters – II. 0016 + 16 at z = 0.54

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Abstract
We have imaged the distant cluster 0016+ 16 (z =0.54) through six intermediate-bandwidth filters ranging in wavelength from 418 to 862 nm, maintaining a photometric precision of 10 per cent to a limiting magnitude of F=22. We find the field-subtracted colour distributions are not compatible with a single uniformly red population of early-type members at z =0.54. A significant intermediate colour component identified with a spectroscopic object at z =0.30 is also present, thus reducing the possibility that the z =0.54 cluster exhibits an excess of blue galaxies. We demonstrate how our six-colour data can be used to individually classify the galaxies by type and approximate redshift and thus we can identify which objects are members of the z=0.54 cluster. On this basis we determine that the richness of the cluster is comparable to that of the Coma cluster, but that the mean spectral energy distribution of the E/S0s appears to be significantly bluer than its present-day equivalent at ultraviolet wavelengths. A sizeable scatter in the far-ultraviolet is also noted and attributed either to variable evolutionary corrections for theE/S0 population or to enhanced star formation in the discs of what may be spiral precursors of present day S0 galaxies. By extending this technique to a new sample of distant clusters we will clarify whether these evolutionary changes are widespread at remote epochs.

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