外压能解释分子云的最新结果吗？
Does External Pressure Explain Recent Results for Molecular Clouds?
摘要：
Heyer等人（2009）最近的论文指出，对星际云的大小、线宽和柱密度的观测结果与简单维里平衡（VE）不一致，简单维里平衡是引力能和动能之间的平衡，因为星际云要么具有太多的动能，要么具有太少的质量而无法束缚。这可能是由Dobbs等人（2011年）提出的VE违反，Heyer等人（2009年）提出的观测低估质量，或由Heyer等人（2004年）提出的外部压力作为额外的约束力。Heyer等人2009年的数据不能用单一的外压值来解释，但如果样品中不同的云具有不同的外压，范围在Pe/k = E4至E7 cm-3 K之间，那么大多数云可能处于压力维里平衡（PVE）。在本文中，我们讨论了两个后果的外部压力。首先，我们表明，观测数据是一致的假设（Chieffie 1987），大多数云是在一个临界质量的动力学稳定性完全由压力决定。超过这个质量的云是不稳定的引力坍缩或分裂。第二，我们表明，外部压力修改了著名的尺寸线宽关系首先提出的Larson（1981），使比例不再是常数，但取决于外部压力。
英文摘要：
The recent paper by Heyer et al (2009) indicates that observations of size, linewidth and column density of interstellar clouds do not agree with simple virial equilibrium (VE) as a balance between gravitational and kinetic energies in the sense that the clouds either have too much kinetic energy or too little mass to be bound. This may be explained by violation of VE as suggested by Dobbs et al 2011, by observational underestimation of the masses as suggested by Heyer et al 2009, or by an external pressure acting as an additional confining force as suggested earlier by Heyer et al 2004. The data of Heyer et al. 2009 cannot be explained with a single value for the external pressure, but if different clouds in the sample have different external pressures in the range of Pe/k = E4 to E7 cm-3 K, then most of the clouds could be in pressure virial equilibrium (PVE). In this paper we discuss two consequences of the external pressure. First, we show that the observational data are consistent with the hypothesis (Chieźe 1987) that most clouds are at a critical mass for dynamical stability determined solely by the pressure. Above this mass a cloud is unstable to gravitational collapse or fragmentation. Second, we show that the external pressure modifies the well-known size-linewidth relationship first proposed by Larson (1981) so that the proportionality is no longer constant but depends on the external pressure.
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