A New View of Cold H I Clouds in the Milky Way
A New View of Cold H I Clouds in the Milky Way
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DOI：
10.1086/309364
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发表时间：
2000-09
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影响因子：
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通讯作者：
S. Gibson;A. R. Taylor;Lloyd A. Higgs;P. Dewdney
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文献类型：
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作者：
S. Gibson;A. R. Taylor;Lloyd A. Higgs;P. Dewdney
我们以前所未有的细节揭示了中性氢的冷银河云。我们的21厘米合成图，从加拿大银河平面调查，显示了众多的和不同的人口的H I自吸收（HISA）功能的气体外的太阳圈。这些对象在大小、形状和相对于背景H I的对比度上变化。所有显示高水平的角和速度结构，大多数会出现显着稀释，如果不是不可见的，在较低分辨率的H I调查。英仙座臂的一些特征仍然没有被我们测量的1'光束所分辨，在2千秒差距的距离上，其视直径小于0.6秒差距。我们检测到的大多数HISA特征没有明显的12 CO排放对应物。这表明，要么HISA不是主要在分子云中发现的，就像过去经常假设的那样，要么CO不是H2的良好示踪剂。一些缺乏CO的HISA显示出远红外尘埃排放，尽管这是否来自屏蔽的分子气体或扩散的原子云尚不清楚。限制HISA的气体性质仍然是一个困难的问题，但我们引入了一种新的方法来帮助这个过程。我们的方法涉及到一些物理参数，通过气体定律和线积分关系，并应证明强大的，如果输入变量是足够众所周知的。我们探讨了目前允许的参数范围为三个样本功能非常不同的外观。我们发现自旋温度约为50 K，密度约为102 cm-3。
We reveal cold Galactic clouds of neutral hydrogen in unprecedented detail. Our 21 cm synthesis maps, taken from the Canadian Galactic Plane Survey, show a numerous and diverse population of H I self-absorption (HISA) features in gas outside the solar circle. These objects vary in size, shape, and contrast against the background H I. All display a high level of angular and velocity structure, and most would appear significantly diluted, if not invisible, in lower resolution H I surveys. A number of Perseus arm features remain unresolved by the 1' beam of our survey, with apparent diameters less than 0.6 pc at 2 kpc distance. The majority of HISA features we detect have no obvious 12CO emission counterparts. This suggests that either HISA is not found predominantly in molecular clouds, as has often been presumed in the past, or that CO is not a good tracer of H2. Some HISA lacking CO shows far-infrared dust emission, though whether this arises from shielded molecular gas or from diffuse atomic clouds is not clear. Constraining the gas properties of HISA remains a difficult problem, but we introduce a new method that aids this process. Our approach relates a number of physical parameters via gas law and line integral relationships and should prove powerful if the input variables are sufficiently well known. We explore the current allowed parameter ranges for three sample features of very different appearance. We find spin temperatures ≲50 K and densities ≳102 cm-3.