Cosmic Ray楼梯：Cosmic Ray声学不稳定的结果
The Cosmic Ray Staircase: the Outcome of the Cosmic Ray Acoustic Instability
摘要：
最近，宇宙射线（CR）已经成为驱动星系风的主要候选者。小规模的过程可以极大地影响全球风的特性。我们运行CR流的两个时刻的模拟，以研究如何声波驱动不稳定的相移CR力和CR加热。我们验证了线性理论增长率。随着声波的非线性增长，它们变陡成一系列准周期性的传播激波;激波处的密度跳跃产生CR瓶颈。传播瓶颈的深度取决于密度跃变和速度，对于快速移动的瓶颈，Δ Pc较小。一系列的瓶颈产生了一个CR楼梯结构，这可以从凸壳结构中理解。系统在新扰动的增长和阶梯合并之间达到一个稳定状态。CR在平台处解耦，但在楼梯跳跃处施加强烈的力和加热。在高原没有CR加热导致冷却、强气压梯度和进一步的冲击。如果瓶颈是静止的，它们可以极大地改变全球流动;如果它们的传播时间与动力学时间相当，它们对全球动量和能量转移的影响是适度的。CR声学不稳定性可能与冷气体和热气体之间的热界面以及星系风有关。与辐射流中不透明度的增加类似，由于瓶颈而导致的CR压力的积聚可以显著增加质量流出速率，最高可达一个数量级。它引发了不寻常形式的热不稳定性，这些冲击可能具有独特的观测特征。
英文摘要：
Recently, cosmic rays (CRs) have emerged as a leading candidate for driving galactic winds. Small-scale processes can dramatically affect global wind properties. We run two-moment simulations of CR streaming to study how sound waves are driven unstable by phase-shifted CR forces and CR heating. We verify linear theory growth rates. As the sound waves grow non-linear, they steepen into a quasi-periodic series of propagating shocks; the density jumps at shocks create CR bottlenecks. The depth of a propagating bottleneck depends on both the density jump and its velocity; ΔP_c is smaller for rapidly moving bottlenecks. A series of bottlenecks creates a CR staircase structure, which can be understood from a convex hull construction. The system reaches a steady state between growth of new perturbations, and stair mergers. CRs are decoupled at plateaus, but exert intense forces and heating at stair jumps. The absence of CR heating at plateaus leads to cooling, strong gas pressure gradients and further shocks. If bottlenecks are stationary, they can drastically modify global flows; if their propagation times are comparable to dynamical times, their effects on global momentum and energy transfer are modest. The CR acoustic instability is likely relevant in thermal interfaces between cold and hot gas, as well as galactic winds. Similar to increased opacity in radiative flows, the build-up of CR pressure due to bottlenecks can significantly increase mass outflow rates, by up to an order of magnitude. It seeds unusual forms of thermal instability, and the shocks could have distinct observational signatures.
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