{"abstract":[{"lang":"eng","text":"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 × 10⁴x–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."}],"article_number":"111","publication_status":"published","publication":"The Astrophysical Journal","doi":"10.3847/1538-4357/ac3509","author":[{"full_name":"Isobe, Yuki","first_name":"Yuki","last_name":"Isobe"},{"full_name":"Ouchi, Masami","first_name":"Masami","last_name":"Ouchi"},{"full_name":"Suzuki, Akihiro","first_name":"Akihiro","last_name":"Suzuki"},{"full_name":"Moriya, Takashi J.","first_name":"Takashi J.","last_name":"Moriya"},{"full_name":"Nakajima, Kimihiko","first_name":"Kimihiko","last_name":"Nakajima"},{"last_name":"Nomoto","full_name":"Nomoto, Ken’ichi","first_name":"Ken’ichi"},{"last_name":"Rauch","first_name":"Michael","full_name":"Rauch, Michael"},{"last_name":"Harikane","full_name":"Harikane, Yuichi","first_name":"Yuichi"},{"full_name":"Kojima, Takashi","first_name":"Takashi","last_name":"Kojima"},{"full_name":"Ono, Yoshiaki","first_name":"Yoshiaki","last_name":"Ono"},{"full_name":"Fujimoto, Seiji","first_name":"Seiji","last_name":"Fujimoto"},{"last_name":"Inoue","first_name":"Akio K.","full_name":"Inoue, Akio K."},{"last_name":"Kim","first_name":"Ji Hoon","full_name":"Kim, Ji Hoon"},{"first_name":"Yutaka","full_name":"Komiyama, Yutaka","last_name":"Komiyama"},{"last_name":"Kusakabe","full_name":"Kusakabe, Haruka","first_name":"Haruka"},{"last_name":"Lee","first_name":"Chien-Hsiu","full_name":"Lee, Chien-Hsiu"},{"first_name":"Michael","full_name":"Maseda, Michael","last_name":"Maseda"},{"orcid":"0000-0003-2871-127X","first_name":"Jorryt J","full_name":"Matthee, Jorryt J","id":"7439a258-f3c0-11ec-9501-9df22fe06720","last_name":"Matthee"},{"last_name":"Michel-Dansac","first_name":"Leo","full_name":"Michel-Dansac, Leo"},{"full_name":"Nagao, Tohru","first_name":"Tohru","last_name":"Nagao"},{"last_name":"Nanayakkara","full_name":"Nanayakkara, Themiya","first_name":"Themiya"},{"last_name":"Nishigaki","first_name":"Moka","full_name":"Nishigaki, Moka"},{"first_name":"Masato","full_name":"Onodera, Masato","last_name":"Onodera"},{"last_name":"Sugahara","first_name":"Yuma","full_name":"Sugahara, Yuma"},{"full_name":"Xu, Yi","first_name":"Yi","last_name":"Xu"}],"_id":"11509","publication_identifier":{"issn":["0004-637X"],"eissn":["1538-4357"]},"type":"journal_article","extern":"1","volume":925,"date_updated":"2022-07-21T05:51:25Z","oa":1,"user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","external_id":{"arxiv":["2108.03850"]},"status":"public","date_created":"2022-07-06T12:01:48Z","month":"01","citation":{"ieee":"Y. Isobe <i>et al.</i>, “EMPRESS. IV. Extremely metal-poor galaxies including very low-mass primordial systems with M∗= 10<sup>4</sup>-10<sup>5</sup>⊙ and 2%–3% (O/H): High (Fe/O) suggestive of metal enrichment by hypernovae/pair-instability supernovae,” <i>The Astrophysical Journal</i>, vol. 925, no. 2. IOP Publishing, 2022.","ama":"Isobe Y, Ouchi M, Suzuki A, et al. EMPRESS. IV. Extremely metal-poor galaxies including very low-mass primordial systems with M∗= 10<sup>4</sup>-10<sup>5</sup>⊙ and 2%–3% (O/H): High (Fe/O) suggestive of metal enrichment by hypernovae/pair-instability supernovae. <i>The Astrophysical Journal</i>. 2022;925(2). doi:<a href=\"https://doi.org/10.3847/1538-4357/ac3509\">10.3847/1538-4357/ac3509</a>","mla":"Isobe, Yuki, et al. “EMPRESS. IV. Extremely Metal-Poor Galaxies Including Very Low-Mass Primordial Systems with M∗= 10<sup>4</sup>-10<sup>5</sup>⊙ and 2%–3% (O/H): High (Fe/O) Suggestive of Metal Enrichment by Hypernovae/Pair-Instability Supernovae.” <i>The Astrophysical Journal</i>, vol. 925, no. 2, 111, IOP Publishing, 2022, doi:<a href=\"https://doi.org/10.3847/1538-4357/ac3509\">10.3847/1538-4357/ac3509</a>.","short":"Y. Isobe, M. Ouchi, A. Suzuki, T.J. Moriya, K. Nakajima, K. Nomoto, M. Rauch, Y. Harikane, T. Kojima, Y. Ono, S. Fujimoto, A.K. Inoue, J.H. Kim, Y. Komiyama, H. Kusakabe, C.-H. Lee, M. Maseda, J.J. Matthee, L. Michel-Dansac, T. Nagao, T. Nanayakkara, M. Nishigaki, M. Onodera, Y. Sugahara, Y. Xu, The Astrophysical Journal 925 (2022).","apa":"Isobe, Y., Ouchi, M., Suzuki, A., Moriya, T. J., Nakajima, K., Nomoto, K., … Xu, Y. (2022). EMPRESS. IV. Extremely metal-poor galaxies including very low-mass primordial systems with M∗= 10<sup>4</sup>-10<sup>5</sup>⊙ and 2%–3% (O/H): High (Fe/O) suggestive of metal enrichment by hypernovae/pair-instability supernovae. <i>The Astrophysical Journal</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/1538-4357/ac3509\">https://doi.org/10.3847/1538-4357/ac3509</a>","ista":"Isobe Y, Ouchi M, Suzuki A, Moriya TJ, Nakajima K, Nomoto K, Rauch M, Harikane Y, Kojima T, Ono Y, Fujimoto S, Inoue AK, Kim JH, Komiyama Y, Kusakabe H, Lee C-H, Maseda M, Matthee JJ, Michel-Dansac L, Nagao T, Nanayakkara T, Nishigaki M, Onodera M, Sugahara Y, Xu Y. 2022. EMPRESS. IV. Extremely metal-poor galaxies including very low-mass primordial systems with M∗= 10<sup>4</sup>-10<sup>5</sup>⊙ and 2%–3% (O/H): High (Fe/O) suggestive of metal enrichment by hypernovae/pair-instability supernovae. The Astrophysical Journal. 925(2), 111.","chicago":"Isobe, Yuki, Masami Ouchi, Akihiro Suzuki, Takashi J. Moriya, Kimihiko Nakajima, Ken’ichi Nomoto, Michael Rauch, et al. “EMPRESS. IV. Extremely Metal-Poor Galaxies Including Very Low-Mass Primordial Systems with M∗= 10<sup>4</sup>-10<sup>5</sup>⊙ and 2%–3% (O/H): High (Fe/O) Suggestive of Metal Enrichment by Hypernovae/Pair-Instability Supernovae.” <i>The Astrophysical Journal</i>. IOP Publishing, 2022. <a href=\"https://doi.org/10.3847/1538-4357/ac3509\">https://doi.org/10.3847/1538-4357/ac3509</a>."},"article_processing_charge":"No","acknowledgement":"We thank the referee for the valuable comments. We are also grateful to Koh Takahashi, Nozomu Tominaga, Chiaki Kobayashi, Yutaka Hirai, and Daichi Kashino for having useful discussions. This paper includes data gathered with the 10 m Keck Telescope located at W. M. Keck Observatory, Hawaii. We thank the staff of Keck Observatory for their help with the observations. The Hyper Suprime-Cam (HSC) collaboration includes the astronomical communities of Japan and Taiwan, and Princeton University. The HSC instrumentation and software were developed by the National Astronomical Observatory of Japan (NAOJ), the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), the University of Tokyo, the High Energy Accelerator Research Organization (KEK), the Academia Sinica Institute for Astronomy and Astrophysics in Taiwan (ASIAA), and Princeton University. Based on data collected at the Subaru Telescope and retrieved from the HSC data archive system, which is operated by the Subaru Telescope and Astronomy Data Center at NAOJ. This work was supported by the joint research program of the Institute for Cosmic Ray Research (ICRR), University of Tokyo. The Cosmic Dawn Center is funded by the Danish National Research Foundation under grant No. 140. S.F. acknowledges support from the European Research Council (ERC) Consolidator Grant funding scheme (project ConTExt, grant No. 648179). This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No. 847523 “INTERACTIONS.” This work is supported by World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan, as well as the KAKENHI Grant-in-Aid for Scientific Research (A; 15H02064, 17H01110, 17H01114, 20H00180, and 21H04467) through the Japan Society for the Promotion of Science (JSPS). This work has been supported in part by JSPS KAKENHI grant Nos. JP17K05382, JP20K04024, and JP21H04499 (K.N.). Yuki Isobe, Kimihiko Nakajima, Yuichi Harikane, Takashi Kojima, and Masato Onodera are supported by JSPS KAKENHI grant Nos. 21J20785, 20K22373,19J01222, 18J12840, and 17K14257, respectively.","oa_version":"Published Version","issue":"2","title":"EMPRESS. IV. Extremely metal-poor galaxies including very low-mass primordial systems with M∗= 10⁴-10⁵⊙ and 2%–3% (O/H): High (Fe/O) suggestive of metal enrichment by hypernovae/pair-instability supernovae","quality_controlled":"1","scopus_import":"1","main_file_link":[{"url":"https://arxiv.org/abs/2108.03850","open_access":"1"}],"language":[{"iso":"eng"}],"intvolume":"       925","date_published":"2022-01-31T00:00:00Z","day":"31","year":"2022","publisher":"IOP Publishing","article_type":"original","keyword":["Space and Planetary Science","Astronomy and Astrophysics"]}