HyGAL：通过观测氘和其他小分子II来表征银河系ISM。用IRAM 30 m望远镜进行吸收线测量
HyGAL: Characterizing the Galactic ISM with observations of hydrides and other small molecules II. The absorption line survey with the IRAM 30 m telescope
摘要：
作为HyGAL平流层天文台红外天文学遗产计划的补充，我们报告的结果，简单分子的扩散和半透明的银河云地面吸收线调查。使用射电天文学研究所毫米（IRAM）的30米望远镜，我们调查了分子线在2毫米和3毫米波长范围内对15毫米连续光源。这些源都是大质量的恒星形成区域，主要位于银河系的第一和第二象限，形成了可以由IRAM 30 m望远镜观察到的HyGAL样本的子集。我们检测到HCO $^+$吸收线朝向14条视线，我们确定了78个前景云成分，以及HCN，HNC，C $_2$ H和c-C $_3$ H $_2$朝向大多数视线的线。此外，CS和H $_2$ S吸收线被发现朝向至少一半的连续谱源。静态Meudon光解离区（PDR）的等压模型，考虑紫外线为主的化学不能再现的所有7个分子物种的柱密度只有几个因素，除了H $_2$ S。湍流耗散驱动的其他形成路线的列入可能解释了观测到的高柱密度，这些物种在弥漫的云。对于较小的样本，H $_2$ S和CS相对于H $_2$的丰度有一个初步趋势，即在弥漫云（$X$（H $_2$ S）和$X$（CS）$\sim 10^{-8} - 10^{-7}$）中比在半透明云（$X$（H $_2$ S）和$X$（CS）$\sim 10^{-9} - 10^{-8}$）中更大;然而，为了证实这一趋势，需要更大的样本。推导出的H $_2$ S柱密度高于等压PDR模型预测的值，表明含硫冰幔中H $_2$ S的化学解吸可能在增加H $_2$ S丰度中起作用。
英文摘要：
As a complement to the HyGAL Stratospheric Observatory for Infrared Astronomy Legacy Program, we report the results of a ground-based absorption line survey of simple molecules in diffuse and translucent Galactic clouds. Using the Institut de Radioastronomie Millimétrique (IRAM) 30 m telescope, we surveyed molecular lines in the 2 mm and 3 mm wavelength ranges toward 15 millimeter continuum sources. These sources, which are all massive star-forming regions located mainly in the first and second quadrants of the Milky Way, form the subset of the HyGAL sample that can be observed by the IRAM 30 m telescope. We detected HCO$^+$ absorption lines toward 14 sightlines, toward which we identified 78 foreground cloud components, as well as lines from HCN, HNC, C$_2$H, and c-C$_3$H$_2$ toward most sightlines. In addition, CS and H$_2$S absorption lines are found toward at least half of the continuum sources. Static Meudon photodissociation region (PDR) isobaric models that consider ultraviolet-dominated chemistry were unable to reproduce the column densities of all seven molecular species by just a factor of a few, except for H$_2$S. The inclusion of other formation routes driven by turbulent dissipation could possibly explain the observed high column densities of these species in diffuse clouds. There is a tentative trend for H$_2$S and CS abundances relative to H$_2$ to be larger in diffuse clouds ($X$(H$_2$S) and $X$(CS) $\sim 10^{-8} - 10^{-7}$) than in translucent clouds ($X$(H$_2$S) and $X$(CS) $\sim 10^{-9} - 10^{-8}$) toward a small sample; however, a larger sample is required in order to confirm this trend. The derived H$_2$S column densities are higher than the values predicted from the isobaric PDR models, suggesting that chemical desorption of H$_2$S from sulfur-containing ice mantles may play a role in increasing the H$_2$S abundance.
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