发表机构
Université de Genève; Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg; Università di Firenze; INAF, Osservatorio di Astrofisica e Scienza dello Spazio; California Institute of Technology; University of Bologna, Department of Physics and Astronomy “Augusto Righi”; Università di Padova; INAF -– Osservatorio Astronomico di Padova; Chiba University（日内瓦大学; 斯特拉斯堡大学，法国国家科学研究中心，斯特拉斯堡天文台; 佛罗伦萨大学; 意大利国家天体物理研究所，空间天体物理学与天体物理观测站; 加州理工学院; 博洛尼亚大学，奥古斯托·里吉物理与天文学系; 帕多瓦大学; 意大利国家天体物理研究所-帕多瓦天文台; 千叶大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
该研究通过ALPINE巡天的3个z~4.5处高[CII]星系，多示踪剂探测分子气体，检验[CII]作为示踪剂的可靠性，发现近太阳金属丰度主序星系的CO相关参数适用，并合星系存在[CII]过量。
AI 中文摘要
高红移星系的分子气体质量通过间接示踪剂推断，但其各自的可靠性仍未得到充分约束。特别是亮[CII] 158μm线目前已被广泛用作z>4处的分子气体示踪剂，但与CO的直接观测检验仍十分稀少。我们从ALPINE巡天中选取3个z~4.5处[CII]光度最高的星系，搜寻其中的CO(4-3)、CO(5-4)和[CI](1-0)线，以评估这些线在高红移主序（MS）星系中的可探测性，并通过对6种示踪剂（CO(4-3)、CO(5-4)、[CI](1-0)、[CII]、尘埃连续谱、基于[CII]的动力学质量）推断出的分子气体质量进行交叉对比，检验[CII]发射作为分子气体示踪剂的可靠性，采用标准校准和转换因子。我们在近太阳金属丰度星系DC873756中高置信度探测到CO(4-3)和CO(5-4)线，在并合系统DC818760中获得CO(4-3)的疑似探测结果，而在半太阳金属丰度星系VC5110377875中未探测到CO发射。[CI]在所有3个星系中均未被探测到。在DC873756中，尽管6种示踪剂各有固有系统误差，但推断出的分子气体质量在不确定性范围内一致。该一致性表明，至少对于z~4.5处的部分近太阳金属丰度MS星系，适用于宇宙正午MS星系的CO SLED和银河系CO-to-H2转换因子仍然适用，且中J CO跃迁可示踪大部分分子气体储库。VC5110377875中未探测到CO与低金属丰度下CO可探测性降低的预期一致。在DC818760中，我们发现基于[CII]的分子气体质量与其他示踪剂推导的质量存在不一致，表明存在[CII]过量，可能反映并合驱动环境中激波和/或弥散电离气体的增强发射。
英文摘要
Molecular gas masses in high-z galaxies are inferred from indirect tracers, whose respective reliability remains poorly constrained. In particular, the bright [CII] 158$μ$m line is now widely used as a molecular gas tracer at z>4, yet direct observational tests against CO remain scarce. We search for CO(4-3), CO(5-4), and [CI](1-0) lines in three of the most [CII]-luminous galaxies at z~4.5 from the ALPINE survey to assess the detectability of these lines in high-z main-sequence (MS) galaxies and to test the reliability of [CII] emission as a molecular gas tracer through the cross-comparison of molecular gas masses inferred from six tracers: CO(4-3), CO(5-4), [CI](1-0), [CII], dust continuum, and [CII]-based dynamical mass, adopting standard calibrations and conversion factors. We detect CO(4-3) and CO(5-4) lines at high significance in the near-solar metallicity galaxy DC873756, obtain a tentative CO(4-3) detection in the merging system DC818760, and detect no CO emission in the half-solar metallicity galaxy VC5110377875. [CI] remains undetected in all three galaxies. In DC873756 the molecular gas masses inferred from the six considered tracers agree within their uncertainties despite different systematics inherent to each tracer. The agreement suggests that, at least for some near-solar metallicity MS galaxies at z~4.5, the CO SLED and Milky Way CO-to-H2 conversion factor adopted for MS galaxies at cosmic noon remain applicable and that mid-J CO transitions trace a substantial fraction of the molecular gas reservoir. The CO non-detection in VC5110377875 is consistent with the reduced CO detectability expected at lower metallicities. In DC818760 we find an inconsistency between the [CII]-based molecular gas mass and masses derived from the other tracers, indicating a [CII] excess possibly reflecting enhanced emission from shocks and/or diffuse ionized gas in merger-driven conditions.
Comments12 pages, 1 page Appendix, 6 figures, 2 tables, submitted to A&A
