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EMPRESS. X. 极贫金属星系中空间分辨的质量—金属度关系：贫金属气体下落供给间歇性恒星形成的证据

EMPRESS. X. Spatially resolved mass-metallicity relation in extremely metal-poor galaxies: evidence of episodic star-formation fueled by a metal-poor gas infall

Kimihiko Nakajima, Masami Ouchi, Yuki Isobe, Yi Xu, Shinobu Ozaki, Tohru Nagao, Akio K. Inoue, Michael Rauch, Haruka Kusakabe, Masato Onodera, Moka Nishigaki, Y… 展开作者

Kimihiko Nakajima, Masami Ouchi, Yuki Isobe, Yi Xu, Shinobu Ozaki, Tohru Nagao, Akio K. Inoue, Michael Rauch, Haruka Kusakabe, Masato Onodera, Moka Nishigaki, Yoshiaki Ono, Yuma Sugahara, Takashi Hattori, Yutaka Hirai, Takuya Hashimoto, Ji Hoon Kim, Takashi J. Moriya, Hiroto Yanagisawa, Shohei Aoyama, Seiji Fujimoto, Hajime Fukushima, Keita Fukushima, Yuichi Harikane, Shun Hatano, Kohei Hayashi, Tsuyoshi Ishigaki, Masahiro Kawasaki, Takashi Kojima, Yutaka Komiyama, Shuhei Koyama, Yusei Koyama, Chien-Hsiu Lee, Akinori Matsumoto, Ken Mawatari, Kentaro Motohara, Kai Murai, Kentaro Nagamine, Minami Nakane, Tomoki Saito, Rin Sasaki, Takatoshi Shibuya, Akihiro Suzuki, Tsutomu T. Takeuchi, Hiroya Umeda, Masayuki Umemura, Kuria Watanabe, Kiyoto Yabe, Hidenobu Yajima, Yechi Zhang

备注：
29 pages, 14 figures. Submitted to ApJ
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AI总结：

研究利用 Subaru/FOCAS IFU 对24个近邻极贫金属星系进行空间分辨分析，发现质量—金属度关系的弥散与 Σ_SFR 相关及贫金属分支，支持贫金属气体下落触发间歇性恒星形成。

摘要：

利用 Subaru/FOCAS IFU 能力，我们考察了近邻宇宙中极贫金属星系（EMPG）内气相金属度、恒星质量与恒星形成率面密度（分别为 Σ_* 和 Σ_SFR）之间的空间分辨关系。我们的分析包括 24 个 EMPG，共 9,179 个 spaxel，覆盖了独特的局域金属度（12+log(O/H)=6.9 至 7.9）和恒星质量面密度（Σ_* 约 10^5 至 10^7 Msun/kpc^2）参数空间，超越了现有大型积分场光谱巡天的范围。通过基于 [NII] BPT 图的空间分辨发射线诊断，我们证实这些 EMPG 中不存在演化的活动星系核。结果表明，尽管分辨的质量—金属度关系在低质量区表现出显著弥散，但该弥散与局域恒星形成面密度密切相关。具体而言，在给定 Σ_* 下，金属度随 Σ_SFR 增加而降低。值得注意的是，半数 EMPG 在分辨的质量—金属度关系上呈现明显的贫金属水平分支。该特征通常出现在具有最高 Σ_* 和 Σ_SFR 的峰值团块处，并被相对富金属的周围区域环绕。这些发现支持贫金属气体下落为 EMPG 中间歇性恒星形成提供燃料的情景，并与这些系统中观测到的运动学性质一致。此外，我们识别出 4 个中心金属度极低（12+log(O/H) ≲ 7.2）的 EMPG，它们只显示贫金属团块而没有周围的富金属区域。这表明此类金属度不足太阳金属度几个百分点的超低金属度 EMPG，可作为星系演化早期阶段星系的有价值类比对象。

英文摘要：

Using the Subaru/FOCAS IFU capability, we examine the spatially resolved relationships between gas-phase metallicity, stellar mass, and star-formation rate surface densities (Sigma_* and Sigma_SFR, respectively) in extremely metal-poor galaxies (EMPGs) in the local universe. Our analysis includes 24 EMPGs, comprising 9,177 spaxels, which span a unique parameter space of local metallicity (12+log(O/H) = 6.9 to 7.9) and stellar mass surface density (Sigma_* ~ 10^5 to 10^7 Msun/kpc^2), extending beyond the range of existing large integral-field spectroscopic surveys. Through spatially resolved emission line diagnostics based on the [NII] BPT-diagram, we verify the absence of evolved active galactic nuclei in these EMPGs. Our findings reveal that, while the resolved mass-metallicity relation exhibits significant scatter in the low-mass regime, this scatter is closely correlated with local star-formation surface density. Specifically, metallicity decreases as Sigma_SFR increases for a given Sigma_*. Notably, half of the EMPGs show a distinct metal-poor horizontal branch on the resolved mass-metallicity relation. This feature typically appears at the peak clump with the highest Sigma_* and Sigma_SFR and is surrounded by a relatively metal-enriched ambient region. These findings support a scenario in which metal-poor gas infall fuels episodic star formation in EMPGs, consistent with the kinematic properties observed in these systems. In addition, we identify four EMPGs with exceptionally low central metallicities (12+log(O/H) <~ 7.2), which display only a metal-poor clump without a surrounding metal-rich region. This suggests that such ultra-low metallicity EMPGs, at less than a few percent of the solar metallicity, may serve as valuable analogs for galaxies in the early stages of galaxy evolution.

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