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arXiv 2008.03531astro-ph.GA
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年轻的大质量恒星形成团的化学结构：（II）秒差距尺度的CO亏损和$\rm HCO^+$的氘分数

The chemical structure of young high-mass star-forming clumps: (II) parsec-scale CO depletion and deuterium fraction of $\rm HCO^+$

S. Feng, D. Li, P. Caselli, F. Du, Y. Lin, O. Sipilä, H. Beuther, Patricio Sanhueza, K. Tatematsu, S. Y. Liu, Q. Zhang, Y. Wang, T. Hogge, I. Jimenez-Serra, X. … 展开作者

S. Feng, D. Li, P. Caselli, F. Du, Y. Lin, O. Sipilä, H. Beuther, Patricio Sanhueza, K. Tatematsu, S. Y. Liu, Q. Zhang, Y. Wang, T. Hogge, I. Jimenez-Serra, X. Lu, T. Liu, K. Wang, Z. Y. Zhang, S. Zahorecz, G. Li, H. B. Liu, J. Yuan

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摘要：

寒冷而致密的分子云的物理和化学性质是理解恒星如何形成的关键。利用IRAM 30 m和NRO 45 m望远镜，对70 m $μ$暗云和亮云（MIAO）进行了多波长线成像观测。在0.1- 0.5 pc的线性分辨率下，本工作详细研究了我们的全样品中四个源（G11.38+0.81，G15.22-0.43，G14.49-0.13，和G34.74-0.12）的秒差距尺度的CO消耗和$\rm HCO^+$氘（D-）分馏。在每个具有$\rm T<20$ K和$n_{\rm H}\rm\sim10^4$ - $\rm 10^5 cm^{-3}$的源中，我们比较了相邻的70个$μ$ m亮团和暗团，发现（1）每个源的$\rm H_2$柱密度和尘埃温度在空间上有很强的相关性，（2）CO同位素谱线和稠密气体示踪剂（如$\rm H^{13}CO^+$和$\rm DCO^+$的1- 0谱线）的空间分布有很强的相关性;（3）$\rm C^{18}O$和$\rm DCO^+$之间的丰度比与源温度表现出强相关性;（4）从较年轻的团块到更进化的团块，$\rm C^{18}O$的消耗因子和$\rm HCO^+$的D-分数均表现出强劲的下降，下降系数超过3;（5）初步的化学模拟结果表明，我们的源区的化学年龄为${\sim}8\times10^4$ yr，这与它们的自由落体时间尺度相当，但小于它们的收缩时间尺度，这表明我们的源可能在动力学和化学上都很年轻。

英文摘要：

The physical and chemical properties of cold and dense molecular clouds are key to understanding how stars form. Using the IRAM 30 m and NRO 45 m telescopes, we carried out a Multiwavelength line-Imaging survey of the 70 $μ$m dark and bright clOuds (MIAO). At a linear resolution of 0.1--0.5 pc, this work presents a detailed study of parsec-scale CO depletion and $\rm HCO^+$ deuterium (D-) fractionation toward four sources (G11.38+0.81, G15.22-0.43, G14.49-0.13, and G34.74-0.12) included in our full sample. In each source with $\rm T<20$ K and $n_{\rm H}\rm\sim10^4$--$\rm 10^5 cm^{-3}$, we compared pairs of neighboring 70 $μ$m bright and dark clumps and found that (1) the $\rm H_2$ column density and dust temperature of each source show strong spatial anticorrelation; (2) the spatial distribution of CO isotopologue lines and dense gas tracers, such as 1--0 lines of $\rm H^{13}CO^+$ and $\rm DCO^+$, are anticorrelated; (3) the abundance ratio between $\rm C^{18}O$ and $\rm DCO^+$ shows a strong correlation with the source temperature; (4) both the $\rm C^{18}O$ depletion factor and D-fraction of $\rm HCO^+$ show a robust decrease from younger clumps to more evolved clumps by a factor of more than 3; and (5) preliminary chemical modeling indicates chemical ages of our sources are ${\sim}8\times10^4$ yr, which is comparable to their free-fall timescales and smaller than their contraction timescales, indicating that our sources are likely dynamically and chemically young.

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