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We present Keck/LRIS follow-up spectroscopy for 13 photometric candidates ofextremely metal poor galaxies (EMPGs) selected by a machine-learning techniqueapplied to the deep (~26 AB mag) optical and wide-area (~500 deg^2) Subaruimaging data in the EMPRESS survey. Nine out of the 13 candidates are EMPGswith an oxygen abundance (O/H) less than ~10% solar value (O/H)_sun, and foursources are contaminants of moderately metal-rich galaxies or no emission-lineobjects. Notably, two out of the nine EMPGs have extremely-low stellar massesand oxygen abundances of 5*10^4--7*10^5 M_sun and 2--3% (O/H)_sun,respectively. With a sample of five EMPGs with (Fe/O) measurements, two (three)of which are taken from this study (the literature), we confirm that two EMPGswith the lowest (O/H) ratios of ~2% (O/H)_sun show high (Fe/O) ratios of ~0.1,close to the solar abundance ratio. Comparing galaxy chemical enrichmentmodels, we find that the two EMPGs cannot be explained by a scenario ofmetal-poor gas accretion/episodic star-formation history due to their low (N/O)ratios. We conclude that the two EMPGs can be reproduced by an inclusion ofbright hypernovae and/or hypothetical pair-instability supernovae (SNe)preferentially produced in a metal-poor environment. This conclusion impliesthat primordial galaxies at z~10 could have a high abundance of Fe that is notoriginated from Type Ia SNe with delays, and that Fe may not serve as a cosmicclock for primordial galaxies.

astrophysical journal/the astrophysical journal

EMPRESS. IV. Extremely Metal-Poor Galaxies (EMPGs) Including Very  Low-Mass Primordial Systems with M*=10^4--10^5 M_sun and 2--3% (O/H)_sun:  High (Fe/O) Suggestive of Metal Enrichment by Hypernovae/Pair-Instability  Supernovae