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We present the results of a wide-field spectroscopic analysis of the galaxypopulation of the massive cluster MACSJ0717.5+3745 and the surroundingfilamentary structure (z=0.55), as part of our systematic study of the 12 mostdistant clusters in the MACS sample. Of 1368 galaxies spectroscopicallyobserved in this field, 563 are identified as cluster members; of those, 203are classified as emission-line galaxies, 260 as absorption-line galaxies, and17 as E+A galaxies (defined by $\frac{H_{\delta}+H_{\gamma}}{2}>6$\AA and nodetection of [OII] and $H_{\beta}$ in emission). The variation of the fractionof emission- and absorption-line galaxies as a function of local projectedgalaxy density confirms the well-known morphology-density relation, and becomesflat at projected galaxy densities less than $\sim 20Mpc^{-2}. Interestingly,16 out of 17 E+A galaxies lie (in projection) within the ram-pressure strippingradius around the cluster core, which we take to be direct evidence ofram-pressure stripping being the primary mechanism that terminatesstar-formation in the E+A population of galaxy clusters. This conclusion issupported by the rarity of E+A galaxies in the filament which rules out galaxymergers as the dominant driver of evolution for E+A galaxies in clusters. Inaddition, we find the 42 e(a) and 27 e(b) member galaxies, i.e., thedusty-starburst and starburst galaxies respectively, to be spread out acrossalmost the entire study area. Their spatial distribution, which shows a strongpreference for the filament region, suggests that starbursts are triggered inrelatively low-density environments as galaxies are accreted from the fieldpopulation.

The spatial distribution of galaxies of different spectral types in the massive intermediate-redshift cluster MACSJ0717.5+3745