Matryoshka运行（II）：大质量星系团中的时间依赖Turbulence统计、随机粒子加速和微物理碰撞
The Matryoshka Run (II): Time Dependent Turbulence Statistics, Stochastic Particle Acceleration and Microphysics Impact in a Massive Galaxy Cluster
摘要：
我们利用Matryoshka运行研究了10 $^{15}M_\odot$星系团的团内介质中结构形成驱动湍流的时间相关统计。我们调查的湍流级联在内部Mpc的压缩和不可压缩的速度分量。流动保持充分发展的湍流的近似条件，其偏离在大约涡流周转时间内稳定。即使在低质量吸积率下，湍流速度色散仍高于$700$ km s $^{-1}$，压缩能量的分数在10%和40%之间。与不可压缩湍流不同，压缩湍流的标准化和斜率在短时间尺度上易受较大变化的影响。一个主要的合并发生在红移$z\simeq0$周围，并伴随着长时间的增强湍流，归因于与物质空间聚集有关的质量吸积的时间聚集。我们测试模型的随机加速压缩模式的起源弥漫无线电发射的星系团。湍流模拟模型约束了这个复杂问题的一个重要未知数，并提出了它对难以捉摸的团内等离子体微观物理的依赖。特别是，等离子体的碰撞和耗散物理的弱冲击的具体情况影响的压缩模式的加速率具有强烈的影响的级联。在这种背景下，射电晕作为一种复杂的现象出现，在这种现象中，一系列作用于越来越小的尺度上的过程在起作用。压缩模式的随机加速度意味着无线电功率和频谱指数与合并核心距离的统计相关性，原则上都可以用无线电测量进行测试。
英文摘要：
We use the Matryoshka run to study the time dependent statistics of structure-formation driven turbulence in the intracluster medium of a 10$^{15}M_\odot$ galaxy cluster. We investigate the turbulent cascade in the inner Mpc for both compressional and incompressible velocity components. The flow maintains approximate conditions of fully developed turbulence, with departures thereof settling in about an eddy-turnover-time. Turbulent velocity dispersion remains above $700$ km s$^{-1}$ even at low mass accretion rate, with the fraction of compressional energy between 10% and 40%. Normalisation and slope of compressional turbulence is susceptible to large variations on short time scales, unlike the incompressible counterpart. A major merger occurs around redshift $z\simeq0$ and is accompanied by a long period of enhanced turbulence, ascribed to temporal clustering of mass accretion related to spatial clustering of matter. We test models of stochastic acceleration by compressional modes for the origin of diffuse radio emission in galaxy clusters. The turbulence simulation model constrains an important unknown of this complex problem and brings forth its dependence on the elusive micro-physics of the intracluster plasma. In particular, the specifics of the plasma collisionality and the dissipation physics of weak shocks affect the cascade of compressional modes with strong impact on the acceleration rates. In this context radio halos emerge as complex phenomena in which a hierarchy of processes acting on progressively smaller scales are at work. Stochastic acceleration by compressional modes implies statistical correlation of radio power and spectral index with merging cores distance, both testable in principle with radio surveys.
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