在受星系力支配的分子气体中开始自引力和恒星形成的模型：II。云环境解耦设置的崩溃瓶颈
A model for the onset of self-gravitation and star formation in molecular gas governed by galactic forces: II. the bottleneck to collapse set by cloud-environment decoupling
摘要：
在Meidt et al.（2018）中，我们表明，单个分子云尺度上的气体运动学不受自引力的支配，但也跟踪起源于宿主星系势中轨道运动的分量。这与观测到的云线宽度一致，云线宽度显示了维里运动随环境的系统变化，指出了星系势的影响。在本文中，我们假设这些运动减缓了气体的坍缩，从而有助于调节恒星的形成。扩展Meidt等人的结果。（2018），我们推导出一个动力学坍缩时间尺度，只有当气体完全与星系势解耦时，它才接近自由落体时间。利用这个时间尺度，我们可以预测自由落体的部分，强烈的自引力气体在整个恒星形成星系的磁盘中的变化。我们还使用这种崩溃的时间尺度来预测的分子气体恒星形成效率，这是从最大的，反馈调节的水平，在存在强耦合的银河系的潜力降低的变化。我们的模型意味着气体只能从星系中分离出来，然后崩溃，并在云层深处有效地形成恒星。我们发现，这自然解释了在银河系CMZ和其他星系中心每单位气体质量恒星形成率的下降。星系瓶颈恒星形成的模型也同意与解决致密气体和恒星形成的星系盘和本地云的性质的观察。
英文摘要：
In Meidt et al. (2018), we showed that gas kinematics on the scale of individual molecular clouds are not dominated by self-gravity but also track a component that originates with orbital motion in the potential of the host galaxy. This agrees with observed cloud line widths, which show systematic variations from virial motions with environment, pointing at the influence of the galaxy potential. In this paper, we hypothesize that these motions act to slow down the collapse of gas and so help regulate star formation. Extending the results of Meidt et al. (2018), we derive a dynamical collapse timescale that approaches the free-fall time only once the gas has fully decoupled from the galactic potential. Using this timescale we make predictions for how the fraction of free-falling, strongly self-gravitating gas varies throughout the disks of star-forming galaxies. We also use this collapse timescale to predict variations in the molecular gas star formation efficiency, which is lowered from a maximum, feedback-regulated level in the presence of strong coupling to the galactic potential. Our model implies that gas can only decouple from the galaxy to collapse and efficiently form stars deep within clouds. We show that this naturally explains the observed drop in star formation rate per unit gas mass in the Milky Way's CMZ and other galaxy centers. The model for a galactic bottleneck to star formation also agrees well with resolved observations of dense gas and star formation in galaxy disks and the properties of local clouds.
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