S20A0088abst

S20A0088

This is a continuous LRIS proposal of our program, the 1st-half of which has been accepted and successfully carried out in S19B. This time, we propose deeper Keck/LRIS spectroscopy for additional 10 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<∼0.03 selected form the wide, deep HSC-SSP data. Our EMPG sample includes galaxies as faint as i∼24 mag, which the previous SDSS survey could not discover. Such a faint, low-mass, metal-poor galaxy is a key population to investigate the early-phase galaxy formation and a driving force of the cosmic reionization. Deep Keck/LRIS spectroscopy enables to detect very faint emission lines including [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 to constrain the FUV radiation of EMPGs with the photoionization models. This program will provide LyC leaker candidates, 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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