EMPRESS. IV. Extremely Metal-poor Galaxies Including Very Low-mass Primordial Systems with M= 104-105Mand 2%-3% (O/H): High (Fe/O) Suggestive of Metal Enrichment by Hypernovae/Pair-instability Supernovae

Yuki Isobe, Masami Ouchi, Akihiro Suzuki, Takashi J. Moriya, Kimihiko Nakajima, Ken'Ichi Nomoto, Michael Rauch, Yuichi Harikane, Takashi Kojima, Yoshiaki Ono, Seiji Fujimoto, Akio K. Inoue, Ji Hoon Kim, Yutaka Komiyama, Haruka Kusakabe, Chien Hsiu Lee, Michael Maseda, Jorryt Matthee, Leo Michel-Dansac, Tohru NagaoThemiya Nanayakkara, Moka Nishigaki, Masato Onodera, Yuma Sugahara, Yi Xu

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2 Citations (Scopus)

Abstract

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.

Original languageEnglish
Article number111
JournalAstrophysical Journal
Volume925
Issue number2
DOIs
Publication statusPublished - 2022 Feb 1

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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