多相气流的物理学：热风中辐射冷却气体云的碎裂
The physics of multiphase gas flows: fragmentation of a radiatively cooling gas cloud in a hot wind
摘要：
银河风呈现出由热扩散相和冷密集相组成的多相结构。在这里，我们提出了高分辨率的理想化模拟的热超音速风与冷云的相互作用与移动网格代码arepo在设置有和没有辐射冷却。我们证明，冷却导致云的大小大于冷却长度的片段在二维和三维模拟（2D和3D）。我们确认了McCourt等人2018年的早期2D模拟，并强调了暴露在热风中的3D云的破碎过程的差异。碎裂过程是量化的朋友的朋友分析破碎的云和密度功率谱。结果表明，当云的初始半径大于冷却长度时，辐射冷却使功率谱指数逐渐增大，并随着时间的增加而增大，直至云完全溶解在热风中。需要大约1 pc的分辨率来揭示100 pc流出云的冷却诱导碎片的影响。因此，国家的最先进的宇宙学变焦模拟环星系介质（CGM）的数量级从解决这个分裂过程的不足。然而，这种物理学是必要的，可靠地模拟观测到的列密度和覆盖部分的莱曼- $α$晕，高速云，和宽线区域的活动星系核。
英文摘要：
Galactic winds exhibit a multiphase structure that consists of hot-diffuse and cold-dense phases. Here we present high-resolution idealised simulations of the interaction of a hot supersonic wind with a cold cloud with the moving-mesh code arepo in setups with and without radiative cooling. We demonstrate that cooling causes clouds with sizes larger than the cooling length to fragment in two- and three-dimensional simulations (2D and 3D). We confirm earlier 2D simulations by McCourt et al. 2018 and highlight differences of the shattering processes of 3D clouds that are exposed to a hot wind. The fragmentation process is quantified with a friends-of-friends analysis of shattered cloudlets and density power spectra. Those show that radiative cooling causes the power spectral index to gradually increase when the initial cloud radius is larger than the cooling length and with increasing time until the cloud is fully dissolved in the hot wind. A resolution of around 1 pc is required to reveal the effect of cooling-induced fragmentation of a 100 pc outflowing cloud. Thus, state-of-the-art cosmological zoom simulations of the circumgalactic medium (CGM) fall short by orders of magnitudes from resolving this fragmentation process. This physics is, however, necessary to reliably model observed column densities and covering fractions of Lyman-$α$ haloes, high-velocity clouds, and broad-line regions of active galactic nuclei.
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