On the survival of cool clouds in the circumgalactic medium
On the survival of cool clouds in the circumgalactic medium
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DOI：
10.1093/mnras/stz3567
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发表时间：
2019-09
影响因子：
4.8
通讯作者：
Zhihui Li;P. Hopkins;J. Squire;C. Hummels
中科院分区：
文献类型：
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作者：
Zhihui Li;P. Hopkins;J. Squire;C. Hummels
我们探讨了冷云在多相环星系介质中的生存。我们重新审视的“云破碎问题”在一个大的调查模拟，包括辐射冷却，自屏蔽，自重力，磁场，各向异性Braginskii传导和粘度（饱和）。我们探索了广泛的参数，包括云的大小，速度，环境温度和密度，以及各种磁场配置和云湍流。我们发现，现实的磁场和湍流对云的生存有较弱的影响，最重要的物理是辐射冷却和传导。自引力和自屏蔽对于最初是吉恩不稳定的云很重要，但在其他方面基本上无关紧要。非自引力的、实际磁化的云分为四种状态：（1）在低柱密度下，云通过传导迅速蒸发;（2）“失效压力约束”状态，即周围的热气体冷却得太快而不能为云提供压力约束;（3）“无限长寿命”状态，在这个状态下，云的寿命变得比在弓形激波中被扫过的气体的冷却时间长，因此云开始吸积和增长;（4）云最终被不稳定性破坏的“经典云破坏”机制。在最后的制度，云的寿命可以超过天真的云粉碎时间，由于传导诱导的压缩。然而，小的和/或缓慢移动的云也可以比云破碎时间更快地蒸发。我们开发了简单的分析模型，解释了模拟云破坏时间在这个政权。
We explore the survival of cool clouds in multiphase circumgalactic media. We revisit the ‘cloud-crushing problem’ in a large survey of simulations including radiative cooling, self-shielding, self-gravity, magnetic fields, and anisotropic Braginskii conduction and viscosity (with saturation). We explore a wide range of parameters including cloud size, velocity, ambient temperature and density, and a variety of magnetic field configurations and cloud turbulence. We find that realistic magnetic fields and turbulence have weaker effects on cloud survival; the most important physics is radiative cooling and conduction. Self-gravity and self-shielding are important for clouds that are initially Jeans-unstable, but largely irrelevant otherwise. Non-self-gravitating, realistically magnetized clouds separate into four regimes: (1) at low column densities, clouds evaporate rapidly via conduction; (2) a ‘failed pressure confinement’ regime, where the ambient hot gas cools too rapidly to provide pressure confinement for the cloud; (3) an ‘infinitely long-lived’ regime, in which the cloud lifetime becomes longer than the cooling time of gas swept up in the leading bow shock, so the cloud begins to accrete and grow; and (4) a ‘classical cloud destruction’ regime, where clouds are eventually destroyed by instabilities. In the final regime, the cloud lifetime can exceed the naive cloud-crushing time owing to conduction-induced compression. However, small and/or slow-moving clouds can also evaporate more rapidly than the cloud-crushing time. We develop simple analytic models that explain the simulated cloud destruction times in this regime.