"How did the cosmic reionization proceed?” is one of the key questions to be answered. Recent JWST rest-frame optical observations reveal that the galaxies at z>6 are distinct from normal galaxies at z∼0−3 but surprisingly resemble so-called Blueberry galaxies (BBs) at 0.02<z<0.05 rather than the Green Pea galaxies at z∼0.3. BBs are characterized by their low stellar mass (106−8 M⊙), low metallicity (7.13<12+log(O/H)<7.98) and strong [OIII] emission ([OIII]/[OII] ratio, O32 > 8 and EW([OIII]) >1000 Å). Our target has a similarly high ionization parameter (qion) to LAEs and their SDSS fiber spectra show prominent HeII emission indicating very massive stars (VMSs) with a mass of >100 M⊙. Considering the ubiquity of VMSs in local LyC leakers and z∼3 LAEs, our sample is by far the best candidate of the local analog of the cosmic reionization drivers. We propose FOCAS IFU observations of five BBs (out of a complete sample of 40 in the SDSS field) as a pilot study. We search for kpc-scale qion structures and compare the distributions of qion and VMSs as well as the HI maps that are obtained with the VLA. This observation will provide us with unique and crucial information on the escaping process of LyC photons and their origin.
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