S19B0053abst
S19B0053
We propose deep Keck/LRIS spectroscopy for 18 extremely metal-poor galaxy (EMPG; ∼0.01–0.1Z⊙) candidates, which are young (<∼30 Myr), low-mass (M⋆∼104–106M⊙) star-forming galaxies at z<∼0.05 selected form the wide, deep HSC-SSP data. Thanks to the HSC data, our EMPG sample includes galaxies as faint as i∼24 mag, which previous shallow surveys (i.g., SDSS; ilim∼21 mag) could not discover. Such a faint, low-mass, metal-poor galaxy is not only a key population to understand the early-phase galaxy formation, but also a strong candidate that drives the cosmic reionization. By the deep Keck/LRIS spectroscopy, we will detect nebular emission lines including very weak [Oiii]4363 and He ii 4686. First, we investigate the physical conditions of ISM such as metallicity, electron density, electron temperature, which are related to the ionization state of ISM. Second, we estimate the spectral hardness and the ionization parameter from He ii4686/Hβ and [Oiii]/[Oii], constraining the FUV radiation of EMPGs with the nebular gas models with photoionization. This program will provide candidates of LyC leakers that show high O32 ratios, for which we will conduct the FUV+NUV spectroscopy with HST/COS to understand the mechanism of the ionization-photon radiation of metal-poor galaxies.
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