超声速冷流场的不稳定性I：体模线性Kelvin-Helmholtz不稳定性
Instability of Supersonic Cold Streams Feeding Galaxies I: Linear Kelvin-Helmholtz Instability with Body Modes
摘要：
在高红移的大质量星系被预测来自宇宙网的狭窄，密集，冷流。这些流以超音速穿过暗物质晕维里半径附近的稳定激波所包围的热介质。我们的长期目标是探索流的加热和耗散率及其碎片化和可能的分裂，以了解星系是如何被喂养的，以及这如何影响它们的恒星形成率和形态。我们在这里提出的第一步，在那里我们分析的线性开尔文-亥姆霍兹不稳定性（KHI）的冷，密集的平板或圆柱体流经热，稀介质在跨音速制度。目前的分析仅限于绝热的情况下，没有重力，并假设在流和介质中的压力相等。通过解析求解的线性色散关系，我们发现从熟悉的快速增长的表面模式在亚音速政权的优势，更缓慢增长的机构模式在超音速政权的过渡。该系统由三个参数参数：流和介质之间的密度差，相对于介质的流速度的马赫数，和相对于晕维里半径的流宽度。我们发现，这些参数的一个现实的选择将流附近的模式转换，与KHI指数增长时间在0.01-10维里交叉时间的范围内的扰动波长相媲美的流宽度。我们证实我们的分析预测与理想化的流体动力学模拟。因此，我们的线性KHI估计表明，KHI可能在原则上是有效的流的演化时，他们到达星系。更明确的结论有待于扩展的非线性制度的分析，包括冷却，热传导，晕势阱，自重力和磁场。
英文摘要：
Massive galaxies at high redshift are predicted to be fed from the cosmic web by narrow, dense, cold streams. These streams penetrate supersonically through the hot medium encompassed by a stable shock near the virial radius of the dark-matter halo. Our long-term goal is to explore the heating and dissipation rate of the streams and their fragmentation and possible breakup, in order to understand how galaxies are fed, and how this affects their star-formation rate and morphology. We present here the first step, where we analyze the linear Kelvin-Helmholtz instability (KHI) of a cold, dense slab or cylinder flowing through a hot, dilute medium in the transonic regime. The current analysis is limited to the adiabatic case with no gravity and assuming equal pressure in the stream and the medium. By analytically solving the linear dispersion relation, we find a transition from a dominance of the familiar rapidly growing surface modes in the subsonic regime to more slowly growing body modes in the supersonic regime. The system is parameterized by three parameters: the density contrast between the stream and the medium, the Mach number of stream velocity with respect to the medium, and the stream width with respect to the halo virial radius. We find that a realistic choice for these parameters places the streams near the mode transition, with the KHI exponential-growth time in the range 0.01-10 virial crossing times for a perturbation wavelength comparable to the stream width. We confirm our analytic predictions with idealized hydrodynamical simulations. Our linear-KHI estimates thus indicate that KHI may in principle be effective in the evolution of streams by the time they reach the galaxy. More definite conclusions await the extension of the analysis to the nonlinear regime and the inclusion of cooling, thermal conduction, the halo potential well, self-gravity and magnetic fields.
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