HyGAL：通过观测氘和其他小分子来表征银河系ISM。W3（OH）、W3 IRS5和NGC 7538 IRS1的调查说明和初步看法
HyGAL: Characterizing the Galactic ISM with observations of hydrides and other small molecules -- I. Survey description and a first look toward W3(OH), W3 IRS5 and NGC 7538 IRS1
摘要：
HyGAL SOFIA遗产计划调查六个氢化物分子- ArH+，OH+，H2O+，SH，OH和CH -和两个原子成分- C+和O -在弥漫的星际介质（ISM）通过吸收线光谱向25个明亮的银河系背景连续源。这项详细的光谱研究旨在利用ISM不同阶段的特定示踪剂和探针的独特价值，正如赫歇尔空间天文台最近的研究所证明的那样。在HyGAL计划下进行的观察将使我们能够解决与ISM中分子材料的生命周期以及影响其相变的物理过程相关的几个问题，例如：（1）ISM中H2馏分的分布函数是什么？(2)低能宇宙射线的电离率在银河系内是如何变化的？(3)星际湍流的本质是什么？是什么机制导致它的消散？本概述讨论了观测策略，与辅助和档案观测的协同作用，采用的数据减少和分析方案，并提出了对三个调查目标，W3（OH），W3 IRS 5和NGC 7538 IRS 1获得的第一批结果。通过对吸收线的广泛观测，对这些气体的柱密度进行了强有力的测量，有助于解决所提出的问题，这些观测结果与理论模型的发展之间存在着及时的协同作用，特别是与湍流ISM中H2的形成有关。因此，提供增强的HyGAL数据产品将作为未来ISM研究的遗产。
英文摘要：
The HyGAL SOFIA legacy program surveys six hydride molecules -- ArH+, OH+, H2O+, SH, OH, and CH -- and two atomic constituents -- C+ and O -- within the diffuse interstellar medium (ISM) by means of absorption-line spectroscopy toward 25 bright Galactic background continuum sources. This detailed spectroscopic study is designed to exploit the unique value of specific hydrides as tracers and probes of different phases of the ISM, as demonstrated by recent studies with the Herschel Space Observatory. The observations performed under the HyGAL program will allow us to address several questions related to the lifecycle of molecular material in the ISM and the physical processes that impact its phase transition, such as: (1) What is the distribution function of the H2 fraction in the ISM? (2) How does the ionization rate due to low-energy cosmic-rays vary within the Galaxy? (3) What is the nature of interstellar turbulence, and what mechanisms lead to its dissipation? This overview discusses the observing strategy, synergies with ancillary and archival observations, the data reduction and analysis schemes adopted; and presents the first results obtained toward three of the survey targets, W3(OH), W3IRS5 and NGC7538IRS1. Robust measurements of the column densities of these hydrides -- obtained through widespread observations of absorption lines-- help address the questions raised, and there is a timely synergy between these observations and the development of theoretical models, particularly pertaining to the formation of H2 within the turbulent ISM. The provision of enhanced HyGAL data products will therefore serve as a legacy for future ISM studies.
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