We employ FOCAS MOS to test “local reionization” around star-forming galaxies in the Epoch of Reionization by evaluating the escape fraction of Lyman-continuum (LyC) photons. For this purpose, we use a dataset from the EIGER survey, a JWST GTO program, conducting slitless spectroscopic galaxy surveys over 5.3<z<7.0 in the fields of z>6 luminous quasars, for which high-quality Lyα forest spectra had been obtained. The program provides high-completeness samples of star-forming galaxies with accurate spectroscopic redshifts. This allows for cross-correlating galaxy distributions with the Lyα/Lyβ forest and thus to identify galaxies which are likely to be responsible for individual transmission spikes, which are a proxy of ionized regions. These findings provide strong evidence that star-forming galaxies play a crucial role in cosmic reionization. However, a critical question remains unanswered: whether these relatively bright detected galaxies, or the fainter undetected galaxies that are spatially co-located, are the ones actually ionizing their surroundings. To address this, we will measure their Lyα emission as a proxy of the escape of LyC photons.
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