THE DEPENDENCE OF STAR FORMATION RATES ON STELLAR MASS AND ENVIRONMENT AT z ∼ 0.8

We examine the star formation rates (SFRs) of galaxies in a redshift slice encompassing the z = 0.834 cluster RX J0152.7-1357. We used a low-dispersion prism in the Inamori Magellan Areal Camera and Spectrograph to identify galaxies with z(AB) < 23.3 mag in diverse environments around the cluster out to projected distances of similar to 8 Mpc from the cluster center. We utilize a mass-limited sample (M > 2 x 10(10) M(circle dot)) of 330 galaxies that were imaged by Spitzer MIPS at 24 mu m to derive SFRs and study the dependence of specific SFR (SSFR) on stellar mass and environment. We find that the SFR and SSFR show a strong decrease with increasing local density, similar to the relation at z similar to 0. Our result contrasts with other work at z similar to 1 that finds the SFR-density trend to reverse for luminosity-limited samples. These other results appear to be driven by star formation (SF) in lower mass systems (M similar to 10(10) M(circle dot)). Our results imply that the processes that shut down SF are present in groups and other dense regions in the field. Our data also suggest that the lower SFRs of galaxies in higher density environments may reflect a change in the ratio of star-forming to non-star-forming galaxies, rather than a change in SFRs. As a consequence, the SFRs of star-forming galaxies, in environments ranging from small groups to clusters, appear to be similar and largely unaffected by the local processes that truncate SF at z similar to 0.8.