The Dynamic Interstellar Medium: A Celebration of the Canadian Galactic Plane Survey
The Dynamic Interstellar Medium: A Celebration of the Canadian Galactic Plane Survey
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发表时间：
2010
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通讯作者：
T. Landecker;S. Gibson
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作者：
T. Landecker;S. Gibson
加拿大银河面巡天为银河系开辟了新的远景，包括冷氢云，它在经典的漫射星际介质和可以形成恒星的引力束缚分子云之间架起了一座关键的桥梁。CGPS和它的同伴IGPS调查显示，这些过渡云以H自吸收（HISA）阴影的形式在银河系H发射背景下惊人地广泛分布。丰富的IGPS数据可以详细检查HISA云的空间结构，气体特性，银河系分布以及与分子气体的对应关系，所有这些都可以约束演化星际介质中冷H云的模型。对具有里程碑意义的IGPS工作的补充是，阿雷西博305米和澳大利亚SKA探路者望远镜将进行新的和即将进行的调查。1. 本综述的范围有限，以便为一些当前的结果留出空间。我们鼓励读者参考较早的评论（Gibson 2002），以及Kulkarni & Heiles（1988）、Dickey & Lockman（1990）和Kalberla & Kerp（2009）的优秀的更广泛的H评论，Wolfire等人（1995,2003）、Cox（2005）和Snow & McCall（2006）的更广泛的ISM评论，以及这些论文集中的许多其他文章。中性原子氢（H）是银盘星际物质的主要组成部分，存在于各种环境中，从T ~ 103−104 K的弥漫气体（热中性介质= WNM）到T ~ 10−102 K的冷云（冷中性介质= CNM）。因此，H21cm线被用于研究环境ISM和密度更大的静止口袋中气体的结构、性质和分布，其中H2形成，这是恒星形成的第一步。本综述的主题CNM观测允许仔细检查(1)原子到分子的相变，(2)由冲击，湍流，可能还有磁场形成的复杂云结构，以及(3)影响H辐射传递的螺旋密度波。加拿大、VLA和南银河面巡天（CGPS: Taylor et al. 2003; VGPS: Stil et al. 2006; SGPS: McClure-Griffiths et al. 2005；合称为“IGPS”）在所有这些方面改变了我们对CNM的看法，为下一代H巡天的未来工作开辟了道路。一个简单的证明WNM和CNM都存在的方法是比较H对紧凑连续源的吸收和H在源附近的发射。这类早期的干涉测量研究（Clark 1965; Radhakrishnan et al. 1972）表明，窄线发射特征具有匹配的窄线吸收，而宽线发射特征缺乏明显的对应吸收，除了在a
The Canadian Galactic Plane Survey has opened new vistas on the Milky Way, including cold hydrogen clouds that bridge a critical gap between the classical diffuse interstellar medium and the gravitationally bound molecular clouds that can form stars. The CGPS and its fellow IGPS surveys revealed these transitional clouds to be surprisingly widespread as H self-absorption (HISA) shadows against the Galactic H emission background. The richness of the IGPS data allows detailed examination of HISA cloud spatial structure, gas properties, Galactic distribution, and correspondence with molecular gas, all of which can constrain models of cold H clouds in the evolving interstellar medium. Augmenting the landmark IGPS effort are new and upcoming surveys with the Arecibo 305m and Australian SKA Pathfinder telescopes. 1. Observational Context This review is of limited scope in order to leave room for a few current results. Readers are encouraged to consult an earlier review (Gibson 2002), as well as excellent broader H reviews by Kulkarni & Heiles (1988), Dickey & Lockman (1990), and Kalberla & Kerp (2009), still-broader ISM reviews by Wolfire et al. (1995, 2003), Cox (2005), and Snow & McCall (2006), and many other articles in these proceedings. Neutral atomic hydrogen (H ), the dominant constituent of interstellar matter in the Galactic disk, is found in a broad range of environments, from diffuse gas with T ∼ 103−104 K (the warm neutral medium = WNM) to cold clouds with T ∼ 10−102 K (the cold neutral medium = CNM). Consequently, the H 21cm line is used to study the structure, properties, and distribution of gas in both the ambient ISM and denser, quiescent pockets where H2 forms, the first step toward star formation. CNM observations, the subject of this review, allow close scrutiny of (1) the atomic-to-molecular phase transition, (2) intricate cloud structure shaped by shocks, turbulence, and perhaps magnetic fields, and (3) spiral density waves that affect H radiative transfer. The Canadian, VLA, and Southern Galactic Plane Surveys (CGPS: Taylor et al. 2003; VGPS: Stil et al. 2006; SGPS: McClure-Griffiths et al. 2005; together, “the IGPS”) have transformed our view of the CNM on all of these fronts, opening the way for future work with the next generation of H surveys. A simple demonstration that both WNM and CNM temperature regimes exist is to compare H absorption toward a compact continuum source with H emission adjacent to the source. Early interferometric studies of this sort (Clark 1965; Radhakrishnan et al. 1972) showed that narrow-line emission features have matching narrow-line absorption, but broad-line emission lacks obvious absorption counterparts, except at a