标题： 红外暗云中的化学 显示英文标题

标题： Chemistry in Infrared Dark Clouds

摘要： 大质量恒星在塑造星系结构中起着重要作用。 红外暗云（IRDCs）由于其低温和高密度，已被确认为大质量恒星的潜在诞生地。 为了理解大质量恒星的形成过程，必须表征红外暗云中的物理和化学条件。 本文的目标是研究南天红外暗云样本的化学组成。 观测的一个重要方面是检查红外暗云中的分子丰度是否与低质量前恒星核相似，或者是否显示出更演化阶段的特征。 我们使用22米Mopra射电望远镜，在86至93 GHz的频率范围内对15个IRDC进行了观测。 我们在所有云中检测到HNC、HCO$^+$和HNC发射，并在所有IRDC中除了一个外检测到N$_2$H$^+$。 在一些云中我们检测到SiO发射。 在所有IRDC中都发现了HCO$^+$发射线轮廓的复杂形状。 这些迹象表明存在吸积和外流运动，以及恒星形成活动的开始，至少在某些IRDC区域如此。 在可能的情况下，我们计算分子丰度，并将其与之前获得的低质量前恒星核和高质量原恒星物体（HMPOs）的值进行比较。 我们显示了IRDCs在单天线观测尺度上具有与低质量前恒星核相似的分子丰度，而不是HMPOs的丰度的趋势。 显示英文摘要

摘要： Massive stars play an important role in shaping the structure of galaxies. Infrared dark clouds (IRDCs), with their low temperatures and high densities, have been identified as the potential birthplaces of massive stars. In order to understand the formation processes of massive stars the physical and chemical conditions in infrared dark clouds have to be characterized. The goal of this paper is to investigate the chemical composition of a sample of southern infrared dark clouds. One important aspect of the observations is to check, if the molecular abuncances in IRDCs are similar to the low-mass pre-stellar cores, or whether they show signatures of more evolved evolutionary stages. We performed observations toward 15 IRDCs in the frequency range between 86 and 93 GHz using the 22-m Mopra radio telescope. We detect HNC, HCO$^+$ and HNC emission in all clouds and N$_2$H$^+$ in all IRDCs except one. In some clouds we detect SiO emission. Complicated shapes of the HCO$^+$ emission line profile are found in all IRDCs. Both signatures indicates the presence of infall and outflow motions and beginning of star formation activity, at least in some parts of the IRDCs. Where possible, we calculate molecular abundances and make a comparison with previously obtained values for low-mass pre-stellar cores and high-mass protostellar objects (HMPOs). We show a tendency for IRDCs to have molecular abundances similar to low-mass pre-stellar cores rather than to HMPOs abundances on the scale of our single-dish observations.