A pair narrow-band filters (SWIMS-NB1244 and HSC-NB921) provides us with a unique opportunity to map the Balmer decrement (Hα/Hβ) at z=0.9 only by imaging observations. We propose to apply this bran-new technique to a gigantic 50Mpc scale supercluster at z∼0.9 which has been newly extended and identified by HSC broad-band imaging and panoramic optical spectroscopy. This unique combination of the technique and the target will enable us for the first time to investigate the environmental dependence of dust extinction (mode of star formation) and star forming activities ever so precisely without a significant selection bias along such a large scale structure (LSS). The major issues to be addressed include where the star forming activities are enhanced and/or quenched as galaxies fall in and assemble to denser regions along the LSS, in particular if the star formation in some galaxies become a dusty starburst mode in cluster outskirts and/or groups as expected by frequent galaxy interactions or mergers probably occurring in such environments at this cosmic epoch. We have already obtained SWIMS NB1244 imaging for 6 fields in S22A. Therefore, in this proposal, we request MOIRCS J,H,Ks band imaging and HSC NB921 imaging to complete this unique project.
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