用CO同位素体追踪自引力气体
Trace the Self-Gravitating Gas Using CO Isotopologues
AI总结：
本研究提出利用多谱线CO同位素体观测，通过$N$-PDF方法可靠追踪分子云内自引力气体，其结果与基于尘埃的方法吻合，为识别恒星形成气体提供了替代方案。
AI中文摘要：
近期研究表明，恒星形成率（SFR）与引力束缚气体的质量呈紧密线性相关，该质量可从尘埃发射观测得到的柱密度概率分布函数（$N$-PDF）的幂律尾部界定。这一关系在银河系内跨越四个数量级成立，涵盖从低质量到高质量恒星形成区，以及中心分子区的极端环境。基于此框架，我们提出一种利用多谱线CO同位素体观测估算分子云内引力束缚气体质量的新方法。我们的样本包含16个在$^{12}$CO、$^{13}$CO和C$^{18}$O $J$=1-0上有可靠探测的分子云，涵盖银河系内部的大质量分子云及邻近恒星形成区。我们发现，结合CO同位素体数据得到的$N$-PDF恢复出了基于尘埃研究中观测到的特征对数正态加幂律分布。在整个样本中，基于尘埃方法和CO方法估算的自引力结构的质量和空间分布吻合良好。这表明CO同位素体组合可通过$N$-PDF方法可靠地追踪自引力组分，为识别分子云中的恒星形成气体提供了一种可靠、可扩展且具有速度分辨率的替代尘埃发射的方法。
英文摘要：
Recent studies have shown that the star formation rate (SFR) correlates tightly and linearly with the mass of gravitationally bound gas, which can be delineated from the power-law tail of the column-density probability distribution function ($N$-PDF) derived from dust emission observations. This relationship holds across four orders of magnitude within the Milky Way--spanning low-mass to high-mass star-forming regions and encompassing the extreme environment of the Central Molecular Zone. Building on this framework, we present a new approach for estimating the mass of gravitationally bound gas in molecular clouds using multi-line CO isotopologue observations. Our sample includes 16 molecular clouds with robust detections in $^{12}$CO, $^{13}$CO, and C$^{18}$O $J$ = 1-0, spanning both massive inner Galaxy clouds and nearby star-forming regions. We find that the $N$-PDFs derived from combined CO isotopologue data recover the characteristic log-normal plus power-law profiles seen in dust-based studies. The mass and spatial distribution of the self-gravitating structures estimated from both dust-based and CO-based methods agree well throughout the sample. This indicates that the CO isotopologue combination can robustly trace the self-gravitating component via the $N$-PDF method and provides a reliable, scalable, and velocity-resolved alternative to dust emission for identifying the star-forming gas in molecular clouds.
