A low global star formation rate in the rich galaxy cluster AC 114 at z=0.32

We present the results of a wide-field survey for H alpha -emitting galaxie s in the cluster AC 114 at z = 0.32. Spectra centered on H alpha at the clu ster redshift have been obtained for 586 galaxies to I-tot similar to 22 ou t to a radius of similar to2 h(50)(-1) Mpc. At most, only similar to 10% of these were found to be H alpha -emitting cluster members. These objects ar e predominantly blue and of late-type spiral morphology, consistent with th em hosting star formation. However, similar to 65% of the cluster members c lassified morphologically as spirals (with HST) have no detectable H alpha emission; star formation and morphological evolution in cluster galaxies ap pear to be largely decoupled. Changes in the H alpha detection rate and the strength of H alpha emission with environment (as traced by local galaxy d ensity) are found to be weak within the region studied. Star formation with in the cluster members is also found to be strongly and uniformly suppresse d with the rates inferred from the H alpha emission not exceeding 4 M-. yr( -1), and AC 114's H alpha luminosity function being an order of magnitude b elow that observed for field galaxies at the same redshift. None of the gal axies detected have the high star formation rates associated with "starburs t" galaxies; however, this may still be reconcilable with the known (8% +/- 3%) fraction of "post-starburst" galaxies within AC 114, given the poorly determined but short lifetimes of starbursts and the possibility that much of the associated star formation is obscured by dust.