(Proposal ID) S11B-114 (PI) Koyama, Yusei (Proposal Title) Physical Origin of Dusty Starbursts in the Cluster Outskirts at z=0.4 (Abstract) We propose integral field spectroscopy with GMOS on Gemini(N) of "dusty red galaxies" in the in-falling groups around the CL0939+47 cluster at z = 0.405. These galaxies have been discovered in our panoramic Halpha survey using a narrow-band filter (NB921) on Suprime-Cam, and they are likely to be in the transitional phase before they eventually evolve into passively evolving early- type galaxies which dominate present-day clusters. In this proposal, by spatially resolving the Halpha emission in these galaxies on 2-3 kpc scales with GMOS IFU observations, we aim to provide an unique resolved view of the influence of the environmental effects on the physical processes within these transforming galaxies. Our goals are: (1) to map out the star-formation activity within individual galaxies using Halpha to determine where intense star formation and hence stellar-build up is occuring (e.g. centrally concetrated or extended throughout disk), and (2) to reveal their kinematics to fully understand the physical origin of these transitional galaxies (e.g. we can distinguish between disordered mergers and regularly rotating disk). Note that we have selected our targets to be secure Halpha-line emitters with known, bright fluxes to ensure these observations are as efficient as possible.