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.
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U2 - 10.3847/1538-4357/ac3509
DO - 10.3847/1538-4357/ac3509
M3 - Article
AN - SCOPUS:85125859845
SN - 0004-637X
VL - 925
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 111
ER -