The Extreme Low-mass End of the Mass–Metallicity Relation at z ∼ 7

Iryna Chemerynska, Hakim Atek, Pratika Dayal, Lukas J. Furtak, Robert Feldmann, Jenny E. Greene, Michael V. Maseda, Themiya Nanayakkara, Pascal A. Oesch, Seiji Fujimoto, Ivo Labbé, Rachel Bezanson, Gabriel Brammer, Sam E. Cutler, Joel Leja, Richard Pan, Sedona H. Price, Bingjie Wang, John R. Weaver and Katherine E. Whitaker
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Abstract

The mass–metallicity relation provides crucial insights into the baryon cycle in galaxies and strong constraints on galaxy formation models. We use JWST NIRSpec observations from the UNCOVER program to measure the gas-phase metallicity in a sample of eight galaxies during the epoch of reionization at z = 6–8. Thanks to the strong lensing of the galaxy cluster Abell 2744, we are able to probe extremely low stellar masses between 106 and 108M⊙. Using strong-line diagnostics and the most recent JWST calibrations, we derive extremely low oxygen abundances in the range of 12 + log(O/H) = 6.7–7.8. By combining this sample with more massive galaxies at similar redshifts, we derive a best-fit relation of 12 + log(O/H) = × , which becomes steeper than determinations at z ∼ 3–6 toward low-mass galaxies. Our results show a clear redshift evolution in the overall normalization of the relation, galaxies at higher redshift having significantly lower metallicities at a given mass. A comparison with theoretical models provides important constraints on which physical processes, such as metal mixing, star formation or feedback recipes, are important in reproducing the observations. Additionally, these galaxies exhibit star formation rates that are higher by a factor of a few to tens compared to extrapolated relations at similar redshifts or theoretical predictions of main-sequence galaxies, pointing to a recent burst of star formation. All these observations are indicative of the highly stochastic star formation and interstellar medium enrichment expected in these low-mass systems, suggesting that feedback mechanisms in high-z dwarf galaxies might be different from those in place at higher masses.
z∼7质量-金属性关系的极低质量端
质量-金属性关系为了解星系中的重子循环提供了重要信息,也为星系形成模型提供了强有力的约束。我们利用 UNCOVER 计划中的 JWST NIRSpec 观测数据,测量了 z = 6-8 再电离时代八个星系样本的气相金属性。由于星系团Abell 2744的强透镜作用,我们能够探测到质量在106-108M⊙之间的极低恒星质量。利用强线诊断和最新的 JWST 定标,我们得出了极低的氧丰度,范围在 12 + log(O/H) = 6.7-7.8 之间。通过把这个样本与类似红移下质量更大的星系结合起来,我们得出了一个最佳拟合关系:12 + log(O/H) = ×,这个关系比 z ∼ 3-6 时对低质量星系的测定结果更加陡峭。我们的结果表明,在这一关系的总体归一化过程中,红移演化非常明显,在给定质量下,红移较高的星系的金属性明显较低。通过与理论模型的比较,我们可以发现哪些物理过程(如金属混合、恒星形成或反馈配方)对再现观测结果非常重要。此外,与类似红移下的外推关系或主序星系的理论预测相比,这些星系的恒星形成率要高出几倍到几十倍,这表明恒星形成是在最近爆发的。所有这些观测结果都表明,在这些低质量系统中,恒星形成和星际介质富集预期是高度随机的,这表明高兹矮星系中的反馈机制可能不同于高质量星系中的反馈机制。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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