S21B0045

This is a resubmission of our highly ranked program, which was not executed due to COVID-19. Despite its importance, the formation of massive stars in the early universe remains mysterious from the observational point of view. Using the local extremely metal-poor galaxies (EMPGs) below Z =0.05 Z_⊙, we have interestingly indicated that EMPGs show a very large iron-to-oxygen abundance ratio Fe/O of the solar value. This could be a signature of hypothetical pair-instability supernovae taken place by massive star (140–300 M_⊙) progenitors. To test this hypothesis with a larger sample of EMPGs, we propose a large spectroscopic investigation of new 15 Subaru/HSC-selected EMPGs at z<∼0.03 (EMPRESS). The high sensitivity at the blue wavelength of Keck/LRIS allows us to detect faint Fe emission together with O and recombination lines of H and He, and to derive the Fe/O ratio. Our aims of this program are (i) to build the largest EMPG sample below 0.05 Z_⊙ and search for the most metal-poor galaxies, and (ii) to test whether the Fe/O value can be explained by the known parameter of delay-time(type-Ia SNe) and supernova yields via model comparisons after checking for another scenario of dust depletion via hydrogen Balmer decrements, in order to discuss the massive-star formation in early galaxies.

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