TY - JOUR

T1 - EMPRESS. IV. Extremely Metal-poor Galaxies Including Very Low-mass Primordial Systems with M∗= 104-105M⊙and 2%-3% (O/H)

T2 - High (Fe/O) Suggestive of Metal Enrichment by Hypernovae/Pair-instability Supernovae

AU - Isobe, Yuki

AU - Ouchi, Masami

AU - Suzuki, Akihiro

AU - Moriya, Takashi J.

AU - Nakajima, Kimihiko

AU - Nomoto, Ken'Ichi

AU - Rauch, Michael

AU - Harikane, Yuichi

AU - Kojima, Takashi

AU - Ono, Yoshiaki

AU - Fujimoto, Seiji

AU - Inoue, Akio K.

AU - Kim, Ji Hoon

AU - Komiyama, Yutaka

AU - Kusakabe, Haruka

AU - Lee, Chien Hsiu

AU - Maseda, Michael

AU - Matthee, Jorryt

AU - Michel-Dansac, Leo

AU - Nagao, Tohru

AU - Nanayakkara, Themiya

AU - Nishigaki, Moka

AU - Onodera, Masato

AU - Sugahara, Yuma

AU - Xu, Yi

N1 - Publisher Copyright: © 2022. The Author(s). Published by the American Astronomical Society.

PY - 2022/2/1

Y1 - 2022/2/1

N2 - We present Keck/LRIS follow-up spectroscopy for 13 photometric candidates of extremely metal-poor galaxies (EMPGs) selected by a machine-learning technique applied to the deep (∼26 AB mag) optical and wide-area (∼500 deg2) Subaru imaging data in the EMPRESS survey. Nine out of the 13 candidates are EMPGs with an oxygen abundance (O/H) less than ∼10% solar value (O/H)⊙, and four sources are contaminants of moderately metal-rich galaxies or no emission-line objects. Notably, two out of the nine EMPGs have extremely low stellar masses and oxygen abundances of 5 × 104-7 × 105 M⊙ and 2%-3% (O/H)⊙, 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 EMPGs with the lowest (O/H) ratios of ∼2% (O/H)⊙ show high (Fe/O) ratios of ∼0.1, close to the solar abundance ratio. Comparing galaxy chemical enrichment models, we find that the two EMPGs cannot be explained by a scenario of metal-poor gas accretion/episodic star formation history due to their low (N/O) ratios. We conclude that the two EMPGs can be reproduced by the inclusion of bright hypernovae and/or hypothetical pair-instability supernovae (SNe) preferentially produced in a metal-poor environment. This conclusion implies that primordial galaxies at z ∼10 could have a high abundance of Fe that did not originate from Type Ia SNe with delays and that Fe may not serve as a cosmic clock for primordial galaxies.

AB - We present Keck/LRIS follow-up spectroscopy for 13 photometric candidates of extremely metal-poor galaxies (EMPGs) selected by a machine-learning technique applied to the deep (∼26 AB mag) optical and wide-area (∼500 deg2) Subaru imaging data in the EMPRESS survey. Nine out of the 13 candidates are EMPGs with an oxygen abundance (O/H) less than ∼10% solar value (O/H)⊙, and four sources are contaminants of moderately metal-rich galaxies or no emission-line objects. Notably, two out of the nine EMPGs have extremely low stellar masses and oxygen abundances of 5 × 104-7 × 105 M⊙ and 2%-3% (O/H)⊙, 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 EMPGs with the lowest (O/H) ratios of ∼2% (O/H)⊙ show high (Fe/O) ratios of ∼0.1, close to the solar abundance ratio. Comparing galaxy chemical enrichment models, we find that the two EMPGs cannot be explained by a scenario of metal-poor gas accretion/episodic star formation history due to their low (N/O) ratios. We conclude that the two EMPGs can be reproduced by the inclusion of bright hypernovae and/or hypothetical pair-instability supernovae (SNe) preferentially produced in a metal-poor environment. This conclusion implies that primordial galaxies at z ∼10 could have a high abundance of Fe that did not originate from Type Ia SNe with delays and that Fe may not serve as a cosmic clock for primordial galaxies.

U2 - 10.3847/1538-4357/ac3509

DO - 10.3847/1538-4357/ac3509

M3 - Journal article

AN - SCOPUS:85125859845

VL - 925

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2

M1 - 111

ER -