对26个红外暗云的TMRT K波段观测：NH $_{3}$，CCS和HC $_{3}$ N
The TMRT K Band Observations towards 26 Infrared Dark Clouds: NH$_{3}$, CCS, and HC$_{3}$N
摘要：
本文介绍了上海天马射电望远镜K波段对26个红外暗云的观测结果。我们同时观察到NH $_{3}$与CCS（2 $_{1}$-1 $_{0}$）和HC $_{3}$ N $J\,$ =2-1的（1，1），（2，2），（3，3）和（4，4）跃迁。该调查将现有的CCS检测到的IRDC样品从8个增加到23个，从而能够更好地统计研究IRDC中碳链分子（CCM）与含氮分子的比例。用新发展的超精细基团比（HFGR）方法拟合NH $_{3}$的反型线，得到气体温度在10 ~ 18 K之间。大多数IRDC的CCS与NH $_{3}$的柱密度比小于10 $^{-2}$，将IRDC与低质量恒星形成区区分开来。我们进行了化学演化模拟的基础上的三相化学模型NAUTILUS。我们测量的CCM和NH $_{3}$之间的柱密度比与模型中$\lesssim$ 10 $^{5}$ yr的化学演化年龄一致。通过对数据和化学模型的比较表明，CCS、HC $_{3}$ N和NH $_{3}$对源的化学演化阶段较为敏感。
英文摘要：
We present one of the first Shanghai Tian Ma Radio Telescope (TMRT) K Band observations towards a sample of 26 infrared dark clouds (IRDCs). We observed the (1,1), (2,2), (3,3), and (4,4) transitions of NH$_{3}$ together with CCS (2$_{1}$-1$_{0}$) and HC$_{3}$N $J\,$=2-1, simultaneously. The survey dramatically increases the existing CCS-detected IRDC sample from 8 to 23, enabling a better statistical study of the ratios of carbon-chain molecules (CCM) to N-bearing molecules in IRDCs. With the newly developed hyperfine group ratio (HFGR) method of fitting NH$_{3}$ inversion lines, we found the gas temperature to be between 10 and 18 K. The column density ratios of CCS to NH$_{3}$ for most of the IRDCs are less than 10$^{-2}$, distinguishing IRDCs from low-mass star-forming regions. We carried out chemical evolution simulations based on a three-phase chemical model NAUTILUS. Our measurements of the column density ratios between CCM and NH$_{3}$ are consistent with chemical evolutionary ages of $\lesssim$10$^{5}$ yr in the models. Comparisons of the data and chemical models suggest that CCS, HC$_{3}$N, and NH$_{3}$ are sensitive to the chemical evolutionary stages of the sources.
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