发表机构
Universidad de Concepción; Millennium Nucleus for Galaxies (MINGAL); Max-Planck-Institut für extraterrestrische Physik; Universidad de Chile; University of Maryland; Joint Space-Science Institute; Max-Planck-Institut für Radioastronomie; Universidad de La Serena; Caltech Owens Valley Radio Observatory; Leibniz-Institut für Astrophysik Potsdam (AIP); Space Telescope Science Institute; Universität zu Köln（康塞普西翁大学; 星系千年核（MINGAL）; 马克斯·普朗克地外物理研究所; 智利大学; 马里兰大学; 联合空间科学研究所; 马克斯·普朗克射电天文学研究所; 拉塞雷纳大学; 加州理工学院欧文斯谷无线电天文台; 波茨坦阿斯特诺物理莱布尼茨研究所（AIP）; 太空望远镜科学研究所; 科隆大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究利用SOFIA和APEX数据，通过[CII]谱线分解，发现小麦哲伦云中约78%的[CII]来自分子气体，CO微弱气体占主导，且转换因子为银河系4.5倍，证明[CII]是低金属丰度下分子气体的关键示踪剂。
AI 中文摘要
在低金属丰度环境中，尘埃丰度的降低削弱了分子云对远紫外辐射的屏蔽作用，增强了CO的光致离解，从而产生延伸的CO微弱或CO暗分子气体。[CII] 158 $\mu$m谱线是这些CO微弱相的关键示踪剂。我们表征了[CII]发射的多相起源，并量化了小麦哲伦云（SMC）多个区域中CO微弱分子气体的比例，SMC是最近的低金属丰度（$\sim 0.2 Z_\odot$）星系。我们结合高光谱分辨率的SOFIA/GREAT和upGREAT [CII]、APEX CO(2-1)以及ASKAP+Parkes H I 21厘米数据，将[CII]分解为其原子和分子贡献。平均而言，$(78\pm 1)\\%$的[CII]强度来源于分子气体，$(18\pm 1)\\%$来源于原子气体。[CII]示踪的H$_2$占总分子气体柱密度的$(77\pm4)\\%$，表明SMC的分子气体储库以CO微弱气体为主。我们推导出在CO发射区域4 pc尺度上的H$_2$-to-CO转换因子$X_{CO}\approx 8.9\times10^{20}$ cm$^{-2}$ (K km s$^{-1}$)$^{-1}$，是银河系标准值的4.5倍。我们发现CO暗比例与总柱密度或$\Sigma_{SFR}$之间没有显著相关性，表明CO微弱比例主要由尘埃和气体屏蔽而非当前恒星形成活动控制。我们的结果表明[CII]是SMC中分子气体的主导示踪剂，并证实了在低金属丰度环境中延伸、稳定的CO微弱分子相的普遍存在。
英文摘要
In low-metallicity environments, reduced dust abundance weakens molecular cloud shielding against far-ultraviolet radiation, enhancing CO photodissociation and producing extended CO-faint or CO-dark molecular gas. The [CII] 158 $μ$m line is a key tracer of these CO-faint phases. We characterize the multiphase origin of [CII] emission and quantify the CO-faint molecular gas fraction across several regions of the Small Magellanic Cloud (SMC), the nearest low-metallicity ($\sim 0.2 Z_\odot$) galaxy. We combine high spectral resolution SOFIA/GREAT and upGREAT [CII], APEX CO(2-1), and ASKAP+Parkes H I 21 cm data to decompose [CII] into its atomic and molecular contributions. On average, $(78\pm 1)\%$ of [CII] intensity originates from molecular gas and $(18\pm 1)\%$ from atomic gas. The [CII]-traced H$_2$ accounts for $(77\pm4)\%$ of the total molecular gas column density, indicating that the SMC molecular reservoir is dominated by CO-faint gas. We derive a H$_2$-to-CO conversion factor $X_{CO}\approx 8.9\times10^{20}$ cm$^{-2}$ (K km s$^{-1}$)$^{-1}$ on 4 pc scales in CO-emitting regions, 4.5 times the canonical Galactic value. We find no significant correlation between the CO-dark fraction and either total column density or $Σ_{SFR}$, suggesting that the CO-faint fraction is primarily governed by dust and gas shielding rather than current star formation activity. Our results demonstrate that [CII] is the dominant tracer of molecular gas in the SMC and confirm the prevalence of an extended, stable CO-faint molecular phase in low-metallicity environments.
Comments14 pages, 8 figure environments (9 image files), 4 tables. Submmited to Astronomy & Astrophysics, received on 30.06.2026, accepted on 30.08.2026
