Growth and structure of multiphase gas in the cloud-crushing problem with cooling
Growth and structure of multiphase gas in the cloud-crushing problem with cooling
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DOI：
10.1093/mnras/staa3610
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发表时间：
2020-08
影响因子：
4.8
通讯作者：
Vijit Kanjilal;Alankar Dutta;P. Sharma
中科院分区：
文献类型：
--
作者：
Vijit Kanjilal;Alankar Dutta;P. Sharma
我们重新审视的问题，密集/冷气体的增长，在云粉碎设置与辐射冷却。稠密云与扩散介质之间的相对运动产生了具有短冷却时间的混合气体湍流边界层。这种混合气体可以解释在环星系介质和星系/恒星/活动星系核外流等各种来源中观察到的吸收/发射线范围的普遍性。最近，Gronke和Oh表明，混合气体的有效辐射冷却可以导致稠密云的持续增长。他们提出了致密气体增长的阈值云大小，这与Li等人和Sparre等人最近的工作相矛盾。这些阈值在性质上是不同的，因为前者是基于混合气体的冷却时间，而后者是基于热气体的冷却时间。我们的模拟与基于混合气体冷却时间的阈值一致。我们认为，辐射云破碎模拟应该运行足够长的时间，以允许致密气体的后期增长，由于冷却的混合气体，但不要太长，背景气体冷却灾难性的。此外，模拟域应该足够大，使得混合气体不会通过边界损失。虽然混合层是大致等压的，但在不同温度下气体的发射率与等压单相稳定冷却流有根本不同。
We revisit the problem of the growth of dense/cold gas in the cloud-crushing set-up with radiative cooling. The relative motion between the dense cloud and the diffuse medium produces a turbulent boundary layer of mixed gas with a short cooling time. This mixed gas may explain the ubiquity of the range of absorption/emission lines observed in various sources such as the circumgalactic medium and galactic/stellar/active galactic nucleus outflows. Recently, Gronke & Oh showed that the efficient radiative cooling of the mixed gas can lead to continuous growth of the dense cloud. They presented a threshold cloud size for the growth of dense gas that was contradicted by the more recent works of Li et al. & Sparre et al. These thresholds are qualitatively different as the former is based on the cooling time of the mixed gas whereas the latter is based on the cooling time of the hot gas. Our simulations agree with the threshold based on the cooling time of the mixed gas. We argue that the radiative cloud-crushing simulations should be run long enough to allow for the late-time growth of the dense gas due to cooling of the mixed gas but not so long that the background gas cools catastrophically. Moreover, the simulation domain should be large enough that the mixed gas is not lost through the boundaries. While the mixing layer is roughly isobaric, the emissivity of the gas at different temperatures is fundamentally different from an isobaric single-phase steady cooling flow.