Balmer 跃变测量追踪 $1<z<4$ 星系对恒星形成主序的偏离（基于 JWST/NIRSpec）
Balmer Break Measurements Trace Departures from the Star-Forming Main Sequence at $1<z<4$ with JWST/NIRSpec
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中文总结 AI 辅助
利用 JWST/NIRSpec 光谱，研究发现 Balmer 跃变强度与近期恒星形成活动反相关，并可作为追踪 $1<z<4$ 星系偏离恒星形成主序的经验诊断指标。
中文摘要 AI 辅助
我们展示了 JWST/NIRSpec PRISM 对 $1<z<4$ 星系的观测，以研究 Balmer 跃变强度（$D_{\rm Balmer}$）与近期恒星形成之间的关系。利用来自 GOODS-S 中 JADES 瞬变巡天的 NIRSpec 光谱，我们测量了 $D_{\rm Balmer}$ 和氢复合线等值宽度，并通过伴随测光数据的谱能量分布（SED）拟合来推断星系性质。我们发现 $D_{\rm Balmer}$ 与 H$\alpha$+[\ion{N}{2}] 的静止系等值宽度之间存在明显的反相关，即跃变更强的星系表现出更弱的星云发射和更低的近期恒星形成活动。$D_{\rm Balmer}$ 还与质量加权恒星年龄相关，支持其作为这些红移处演化恒星族群经验示踪物的用途。由 H$\alpha$、Pa$\gamma$ 和 SED 拟合推断的恒星形成率大体一致，其弥散可能部分由尘埃消光、谱线测量不确定性和各指标所探测的不同时标驱动。具有更强 $D_{\rm Balmer}$ 的星系在固定恒星质量下也往往更远离恒星形成主序，表明 $D_{\rm Balmer}$ 与近期恒星形成的抑制有关。相比之下，我们发现 $D_{\rm Balmer}$ 与 SED 导出的尘埃消光之间仅存在弱关系，表明尘埃并非所观测趋势的主要驱动因素。这些结果表明，$D_{\rm Balmer}$ 结合复合线测量，是诊断宇宙正午时期星系从恒星形成族群转变的有用经验工具。
英文摘要
We present JWST/NIRSpec PRISM observations of galaxies at $1<z<4$ to study the relation between Balmer-break strength ($D_{\rm Balmer}$) and recent star formation. Using NIRSpec spectra from the JADES Transient Survey in GOODS-S, we measure $D_{\rm Balmer}$ and hydrogen recombination-line equivalent widths, and infer galaxy properties through spectral energy distribution (SED) fitting of the accompanying photometry. We find a clear anti-correlation between $D_{\rm Balmer}$ and the rest-frame equivalent width of H$α$+[\ion{N}{2}], such that galaxies with stronger breaks show weaker nebular emission and lower recent star formation activity. $D_{\rm Balmer}$ also correlates with mass-weighted stellar age, supporting its use as an empirical tracer of evolved stellar populations at these redshifts. Star formation rates inferred from H$α$, Pa$γ$, and SED fitting are broadly consistent, with scatter likely driven in part by dust attenuation, line-measurement uncertainties, and the different timescales probed by each indicator. Galaxies with stronger $D_{\rm Balmer}$ also tend to lie further below the star-forming main sequence at fixed stellar mass, indicating that $D_{\rm Balmer}$ is linked to recent suppression of star formation. In contrast, we find only a weak relation between $D_{\rm Balmer}$ and SED-derived dust attenuation, suggesting that dust is not the main driver of the observed trends. These results show that $D_{\rm Balmer}$, combined with recombination-line measurements, is a useful empirical diagnostic of galaxies transitioning away from the star-forming population at cosmic noon.
发表机构
- University of Illinois Urbana-Champaign（伊利诺伊大学厄巴纳-香槟分校）
- Steward Observatory, University of Arizona（亚利桑那大学斯图尔德天文台）
- Scuola Normale Superiore（意大利高等师范学院）
- Kavli Institute for Cosmology, University of Cambridge（剑桥大学卡弗里宇宙学研究所）
- Cavendish Laboratory, University of Cambridge（剑桥大学卡文迪许实验室）
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