星系团中的浮力不稳定性：绝热宇宙射线对流和各向异性热传导
Buoyancy Instabilities in Galaxy Clusters: Convection Due to Adiabatic Cosmic Rays and Anisotropic Thermal Conduction
摘要：
使用线性稳定性分析和二维和三维的非线性模拟，我们研究的物理浮力不稳定性相结合的热和相对论性（宇宙射线）等离子体，激发的应用程序的星系团。我们认为，宇宙射线的扩散很可能是缓慢的浮力时间相比，在大的长度尺度，使宇宙射线是有效的绝热。如果宇宙线压力$p_{cr}$是热压力的$\gtrsim 25 %$，并且宇宙线熵（$p_{\rm cr}/ρ^{4/3}$; $ρ$是热等离子体密度）向外减小，则宇宙射线驱动类似于恒星中史瓦西对流的绝热对流不稳定性。星系团核心的全球模拟显示，这种不稳定性通过降低宇宙射线熵梯度和驱动有效的对流和湍流混合而饱和。在团核较大半径处，热等离子体不稳定于热通量驱动的浮力不稳定性（HBI）、各向异性热传导产生的对流不稳定性和背景热传导通量。宇宙射线驱动的对流和HBI可能有助于重新分配1a型超新星在星团中产生的金属。我们的计算表明，绝热模拟的星系团可以人为地抑制热等离子体和相对论等离子体的混合;各向异性热传导允许更有效的混合，这可能有助于宇宙射线分布在整个集群体积。
英文摘要：
Using a linear stability analysis and two and three-dimensional nonlinear simulations, we study the physics of buoyancy instabilities in a combined thermal and relativistic (cosmic ray) plasma, motivated by the application to clusters of galaxies. We argue that cosmic ray diffusion is likely to be slow compared to the buoyancy time on large length scales, so that cosmic rays are effectively adiabatic. If the cosmic ray pressure $p_{cr}$ is $\gtrsim 25 %$ of the thermal pressure, and the cosmic ray entropy ($p_{\rm cr}/ρ^{4/3}$; $ρ$ is the thermal plasma density) decreases outwards, cosmic rays drive an adiabatic convective instability analogous to Schwarzschild convection in stars. Global simulations of galaxy cluster cores show that this instability saturates by reducing the cosmic ray entropy gradient and driving efficient convection and turbulent mixing. At larger radii in cluster cores, the thermal plasma is unstable to the heat flux-driven buoyancy instability (HBI), a convective instability generated by anisotropic thermal conduction and a background conductive heat flux. Cosmic-ray driven convection and the HBI may contribute to redistributing metals produced by Type 1a supernovae in clusters. Our calculations demonstrate that adiabatic simulations of galaxy clusters can artificially suppress the mixing of thermal and relativistic plasma; anisotropic thermal conduction allows more efficient mixing, which may contribute to cosmic rays being distributed throughout the cluster volume.
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