Hα‐derived Star Formation Rates for Threez≃0.75 EDisCS Galaxy Clusters

We present Halpha-derived star-formation rates (SFRs) for three z ~ 0.75galaxy clusters. Our 1 sigma flux limit corresponds to a star-formation rate of0.10-0.24 solar mass per year, and our minimum reliable Halpha + [N II]rest-frame equivalent width is 10\AA. We show that Halpha narrowband imaging isan efficient method for measuring star formation in distant clusters. In twoout of three clusters, we find that the fraction of star-forming galaxiesincreases with projected distance from the cluster center. We also find thatthe fraction of star-forming galaxies decreases with increasing local galaxysurface density in the same two clusters. We compare the median rate of starformation among star-forming cluster galaxies to a small sample of star-formingfield galaxies from the literature and find that the median cluster SFRs are\~50% less than the median field SFR. We characterize cluster evolution interms of the mass-normalized integrated cluster SFR and find that the z ~ 0.75clusters have more SFR per cluster mass on average than the z <= 0.4 clustersfrom the literature. The interpretation of this result is complicated by thedependence of the mass-normalized SFR on cluster mass and the lack ofsufficient overlap in the mass ranges covered by the low and high redshiftsamples. We find that the fraction and luminosities of the brightest starburstgalaxies at z ~ 0.75 are consistent with their being progenitors of thepost-starburst galaxies at z ~ 0.45 if the post-starburst phase lasts several(~5) times longer than the starburst phase.Comment: Accepted for publication in ApJ, 20 pages, 24 figure