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arXiv 2006.15413astro-ph.GAastro-ph.SR
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高质量恒星形成区复杂有机分子的演化研究

Evolutionary study of complex organic molecules in high-mass star-forming regions

A. Coletta, F. Fontani, V. M. Rivilla, C. Mininni, L. Colzi, Á. Sánchez-Monge, M. T. Beltrán

备注：
27 pages, 14 figures, 20 tables - Accepted for publication in A&A on 25 June 2020
发表信息：
A&A 641, A54 (2020)
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摘要：

我们研究了四个复杂的有机分子（COMs），甲酸甲酯（$CH_3OCHO$），二甲醚（$CH_3OCH_3$），甲酰胺（$NH_2CHO$），和乙基氰（$C_2H_5CN$），对一个大样本的39个高质量的恒星形成区域代表不同的演化阶段，从早期到演化阶段。我们的目标是确定分子之间的潜在相关性，并通过恒星形成过程追踪它们的进化序列。我们分析了在3，2，和0.9毫米的IRAM-30米望远镜获得的光谱。通过拟合分子线，推导出每个物种的主要物理参数。我们对它们进行了比较，并评估了它们的演变，同时也考虑了其他几个星际环境。我们报告检测20个来源，揭示了一个明确的灰尘吸收柱密度的影响。导出的丰度为$CH_3OCHO$和$CH_3OCH_3$的~ $10^{-10}-10^{-7}$、$NH_2CHO$的~ $10^{-12}-10^{-10}$和$C_2H_5CN$的~ $10^{-11}-10^{-9}$。$CH_3OCHO$、$CH_3OCH_3$和$C_2H_5CN$的丰度在~4个数量级上具有非常强的相关性（r>0.92）。$CH_3OCHO$和$CH_3OCH_3$在大多数参数中显示出最强的相关性，并且对于各种各样的来源，在显著的~9个数量级的光度上显示出几乎恒定的比率（~1）：前恒星到演化的核心，低质量到高质量的物体，冲击，银河系云和彗星。这表明COMs化学可能是早期发展的，然后通过进化阶段保存下来。此外，分子丰度显然随着进化而增加。我们认为$CH_3OCHO$和$CH_3OCH_3$最有可能是化学连接的：例如，它们可以共享一个共同的前体，或者由另一个形成。我们提出了一个一般的情况下，所有的COM，涉及在寒冷的形成，恒星形成的最早阶段，并随后增加解吸与渐进加热的不断发展的核心。

英文摘要：

We have studied four complex organic molecules (COMs), methyl formate ($CH_3OCHO$), dimethyl ether ($CH_3OCH_3$), formamide ($NH_2CHO$), and ethyl cyanide ($C_2H_5CN$), towards a large sample of 39 high-mass star-forming regions representing different evolutionary stages, from early to evolved phases. We aim to identify potential correlations between the molecules and to trace their evolutionary sequence through the star formation process. We analysed spectra obtained at 3, 2, and 0.9 mm with the IRAM-30m telescope. We derived the main physical parameters for each species by fitting the molecular lines. We compared them and evaluated their evolution, also taking several other interstellar environments into account. We report detections in 20 sources, revealing a clear dust absorption effect on column densities. Derived abundances are ~$10^{-10}-10^{-7}$ for $CH_3OCHO$ and $CH_3OCH_3$, ~$10^{-12}-10^{-10}$ for $NH_2CHO$, and ~$10^{-11}-10^{-9}$ for $C_2H_5CN$. The abundances of $CH_3OCHO$, $CH_3OCH_3$, and $C_2H_5CN$ are very strongly correlated (r>0.92) across ~4 orders of magnitude. $CH_3OCHO$ and $CH_3OCH_3$ show the strongest correlations in most parameters, and a nearly constant ratio (~1) over a remarkable ~9 orders of magnitude in luminosity for a wide variety of sources: pre-stellar to evolved cores, low- to high-mass objects, shocks, Galactic clouds, and comets. This indicates that COMs chemistry is likely early developed and then preserved through evolved phases. Moreover, the molecular abundances clearly increase with evolution. We consider $CH_3OCHO$ and $CH_3OCH_3$ to be most likely chemically linked: they could e.g. share a common precursor, or be formed one from the other. We propose a general scenario for all COMs, involving a formation in the cold, earliest phases of star formation and a following increasing desorption with the progressive heating of the evolving core.

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