发表机构
European Southern Observatory; Centro de Astrobiología (CAB), CSIC-INTA; Research School of Astronomy and Astrophysics, Australian National University; Leiden Observatory, Leiden University; Purple Mountain Observatory, Chinese Academy of Sciences; Department of Astronomy, University of Florida; Department of Astronomy, University of Massachusetts, Amherst（欧洲南方天文台; 天体生物学中心（CAB），西班牙国家研究委员会-国家航空航天技术研究所; 澳大利亚国立大学天文与天体物理研究学院; 莱顿大学莱顿天文台; 中国科学院紫金山天文台; 佛罗里达大学天文学系; 马萨诸塞大学阿默斯特分校天文学系）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
基于ACE巡天数据，发现低质量低金属星系遵循分子气体标度关系，分子气体是恒星形成主驱动，并给出新经验公式。
AI 中文摘要
分子气体在调控恒星形成和星系演化中起着核心作用，然而在宇宙正午时期的观测约束仍偏向于大质量、富金属系统。我们展示了来自ALMA化学演化（ACE）大型巡天项目在z~2-2.5处26个未透镜恒星形成星系的CO J=3-2跃迁的ALMA Band 3观测，探测的恒星质量范围为$10^{9} < M_\star < 10^{10.5}\\,\mathrm{M}_{\odot}$，亚太阳金属丰度（8.2 < 12 + log(O/H) < 8.6）。我们使用依赖于金属丰度的CO-to-H$_2$转换因子推导了分子气体质量，并同时分析了叠加测量和涵盖本地及高红移星系的同质化文献汇编。我们发现ACE星系将已建立的分子气体标度关系延伸至比宇宙正午先前探索的恒星质量低一个数量级的范围。分子气体质量（$M_{\rm mol}$）与恒星形成率（SFR）紧密相关，而分子气体分数则表现出对恒星形成主序的比恒星形成率（sSFR）和偏离度的强依赖性。相比之下，分子气体分数与恒星质量仅呈现弱趋势，且与金属丰度无显著依赖关系。分子气体耗尽时间约为1 Gyr，随恒星质量或金属丰度变化很小，随sSFR和偏离恒星形成主序的程度变化较弱。这些结果进一步强化了分子气体的可用性是星系中SFR的主要驱动因素，而恒星形成效率的变化起次要作用。利用ACE和文献样本所探测的扩展参数空间，我们推导了一个新的经验公式，用于根据SFR和sSFR预测$M_{\rm mol}$。观测到的标度关系的持续性表明，存在一个在很大程度上普适的框架，支配着分子气体-恒星形成循环在整个宇宙时间中的运行。
英文摘要
Molecular gas plays a central role in regulating star formation and galaxy evolution, yet observational constraints at cosmic noon remain biased toward massive, metal-rich systems. We present ALMA Band 3 observations of the CO J=3-2 transition in 26 unlensed star-forming galaxies from the ALMA Chemical Evolution (ACE) Large Program at z~2-2.5, probing stellar masses of $10^{9} < M_\star < 10^{10.5}\,\mathrm{M}_{\odot}$ and sub-solar metallicities (8.2 < 12 + log(O/H) < 8.6). We derived molecular gas masses using a metallicity-dependent CO-to-H$_2$ conversion factor and alongside analysed stacking measurements and a homogenized literature compilation spanning both local and high-redshift galaxies. We find that the ACE galaxies extend established molecular-gas scaling relations to an order of magnitude lower stellar masses than previously explored at cosmic noon. The molecular gas mass ($M_{\rm mol}$) correlates tightly with star formation rate (SFR), while molecular gas fractions show a strong dependence on specific star formation rate (sSFR) and offset from the star-forming main sequence. In contrast, molecular gas fractions show only weak trends with stellar mass and no significant dependence on metallicity. Molecular gas depletion times are ~1 Gyr and vary little with stellar mass or metallicity, and weakly with sSFR and offset from the star-forming main sequence. Together this further reinforces that the availability of molecular gas is the primary driver of the SFR in galaxies, with changes in star-formation efficiency playing a secondary role. Leveraging the expanded parameter space probed by the ACE and literature samples, we derive a new empirical prescription for predicting $M_{\rm mol}$ as a function of SFR and sSFR. The persistence of the observed scaling relations suggests a largely universal framework governing the molecular gas-star formation cycle across cosmic time.
CommentsSubmitted to A&A. This paper is one of several companion papers submitted to arXiv simultaneously; see also Shivaei et al., Langan et al, Solimano et al, Geesink et al. Comments welcome
