The Lyα, as one of the most intense emission lines in distant galaxies, is used for various aspects in astronomy; however, the physical interpretation of the observed Lyα flux alone is not simple due to its characteristic of being scattered by Hi resonance. Simultaneous detection of both Hα, which does not resonantly scatter, and Lyα would improve our understanding for various important topics. We propose to use a Subaru/HSC narrow-band(NB) filter, NB872, which can detect the Lyα emission just when the Hα emission enters into the JWST NB-filter F470N at z=6.174. We propose to take HSC NB872 imaging on the CEERS and COSMOS-web regions, where Hα emitter counterparts can be selected on-going and future JWST F470N observations. In the program, 1) we will make a direct measurement on the Lyα escape fraction at the highest-z, for the first time, systematically for a large sample to see the fescLyα dependence on halaxy properties and environments, and 2) discover the candidates of first galaxy and first black hole among dual Hα-Lyα emitters. This is a great opportunity for Subaru with its unique NB imaging capability to contribute to the community legacy survey led by JWST.
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