Hα STAR FORMATION RATES OF z > 1 GALAXY CLUSTERS IN THE IRAC SHALLOW CLUSTER SURVEY

We present Hubble Space Telescope near-IR spectroscopy for 18 galaxy clusters at 1.0 < z < 1.5 in the IRAC Shallow Cluster Survey. We use Wide Field Camera 3 grism data to spectroscopically identify H alpha emitters in both the cores of galaxy clusters as well as in field galaxies. We find a large cluster-to-cluster scatter in the star formation rates within a projected radius of 500 kpc, and many of our clusters (similar to 60%) have significant levels of star formation within a projected radius of 200 kpc. A stacking analysis reveals that dust reddening in these star-forming galaxies is positively correlated with stellar mass and may be higher in the field than the cluster at a fixed stellar mass. This may indicate a lower amount of gas in star-forming cluster galaxies than in the field population. Also, H alpha equivalent widths of star-forming galaxies in the cluster environment are still suppressed below the level of the field. This suppression is most significant for lower mass galaxies (log M-* < 10.0 M-circle dot). We therefore conclude that environmental effects are still important at 1.0 < z < 1.5 for star-forming galaxies in galaxy clusters with log M-* less than or similar to 10.0 M-circle dot.