TURBULENCE IN GALAXY CLUSTER CORES: A KEY TO CLUSTER BIMODALITY?
TURBULENCE IN GALAXY CLUSTER CORES: A KEY TO CLUSTER BIMODALITY?
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星系团核心的湍流：星系团双峰性的关键？
DOI：
10.1088/2041-8205/712/2/l194
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
P. Sharma
中科院分区：
文献类型：
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作者：
I. Parrish;E. Quataert;P. Sharma
我们使用包括磁场、各向异性热传导和辐射冷却在内的三维数值模拟来研究外部施加的湍流对星系团核心热特性的影响。施加的“搅拌”粗略地近似于星系尾流、星系穿过星系团内介质产生的波和/或中央活动星系核产生的湍流的影响。模拟的簇表现出很强的双峰性。适度的湍流水平，〜100 km s−1〜10％的声速，抑制热通量驱动的浮力不稳定性（HBI），导致各向同性的缠结磁场和准稳定的高熵热平衡，没有冷却灾难。热传导主导着团簇核心的加热，但湍流混合至关重要，因为它抑制了 HBI 和（在较小程度上）热不稳定性。较低水平的湍流混合（≲100km s−1）不足以抑制 HBI，迅速导致热失控和冷核团簇。值得注意的是，星系团核心湍流水平的微小波动可以引发冷核心（低熵）和非冷核心（高熵）状态之间的转变。
We study the effects of externally imposed turbulence on the thermal properties of galaxy cluster cores, using three-dimensional numerical simulations including magnetic fields, anisotropic thermal conduction, and radiative cooling. The imposed “stirring” crudely approximates the effects of galactic wakes, waves generated by galaxies moving through the intracluster medium, and/or turbulence produced by a central active galactic nucleus. The simulated clusters exhibit a strong bimodality. Modest levels of turbulence, ∼100 km s−1 ∼ 10% of the sound speed, suppress the heat-flux-driven buoyancy instability (HBI), resulting in an isotropically tangled magnetic field and a quasi-stable, high entropy, thermal equilibrium with no cooling catastrophe. Thermal conduction dominates the heating of the cluster core, but turbulent mixing is critical because it suppresses the HBI and (to a lesser extent) the thermal instability. Lower levels of turbulent mixing (≲100 km s−1) are insufficient to suppress the HBI, rapidly leading to a thermal runaway and a cool-core cluster. Remarkably, then, small fluctuations in the level of turbulence in galaxy cluster cores can initiate transitions between cool-core (low entropy) and non-cool-core (high entropy) states.