A Low Global Star Formation Rate in the Rich Galaxy Cluster AC 114 atz = 0.32

We present the results of a wide-field survey for H-alpha emitting galaxiesin the cluster AC114 at z=0.32. Spectra centred on H-alpha at the clusterredshift have been obtained for 586 galaxies to I~22 out to a radius around2Mpc. At most, only ~10% of these were found to be H-alpha-emitting clustermembers. These objects are predominantly blue and of late-type spiralmorphology, consistent with them hosting star formation. However, ~65% of thecluster members classified morphologically as spirals (with HST), have nodetectable H-alpha emission; star-formation and morphological evolution incluster galaxies appear to be largely decoupled. Changes in the H-alphadetection rate and the strength of H-alpha emission with environment are foundto be weak within the region studied. Star formation within the cluster membersis also found to be strongly and uniformly suppressed, with the rates inferredfrom the H-alpha emission not exceeding 4Mo/yr, and AC114's H-alpha luminosityfunction being an order of magnitude below that observed for field galaxies atthe same redshift. None of the galaxies detected have the high star formationrates associated with `starburst' galaxies; however, this may still bereconciliable with the known (8+/-3%) fraction of `post-starburst' galaxieswithin AC114, given the poorly determined but short lifetimes of starbursts andthe possibility that much of the associated star formation is obscured by dust.Comment: ApJ in press, 11 pages, 8 figures, 1 electronic table included in sourc