Hα-derived star formation rates for three z≃0.75 EDisCS galaxy clusters

We present H alpha-derived SFRs for three z similar or equal to 0.75 galaxy clusters. Our 1 sigma flux limit corresponds to a star formation rate (SFR) of 0.10 - 0.24 h(100)(-2) M(circle dot)yr(-1), and our minimum reliable H alpha + [N II] rest-frame equivalent width is 10 angstrom. We show that H alpha narrowband imaging is an efficient method for measuring star formation in distant clusters. In two out of three clusters, we find that the fraction of star-forming galaxies increases with projected distance from the cluster center. We also find that the fraction of star-forming galaxies decreases with increasing local galaxy surface density in the same two clusters. We compare the median rate of star formation among star-forming cluster galaxies to a small sample of star-forming field galaxies from the literature and find that the median cluster SFRs are similar to 50% less than the median field SFR. We characterize cluster evolution in terms of the mass-normalized integrated cluster SFR and find that the z similar or equal to 0: 75 clusters have more SFR per cluster mass on average than the z <= 0: 4 clusters from the literature. The interpretation of this result is complicated by the dependence of the mass-normalized SFR on cluster mass and the lack of sufficient overlap in the mass ranges covered by the low- and high-redshift samples. We find that the fraction and luminosities of the brightest starburst galaxies at z similar or equal to 0: 75 are consistent with their being progenitors of the poststarburst galaxies at z similar or equal to 0.45 if the poststarburst phase lasts several (similar to 5) times longer than the starburst phase.