arXiv 1201.07542012-01-03astro-ph.COastro-ph.HE

各向异性粘度对Turbulence和团内介质热输运的影响

The Effects of Anisotropic Viscosity on Turbulence and Heat Transport in the Intracluster Medium

Ian J. Parrish, Michael McCourt, Eliot Quataert, Prateek Sharma

备注：: Submitted to MNRAS. Comments are welcome
DOI：: 10.1111/j.1365-2966.2012.20650.x

摘要：

在星系团的团内介质（ICM）中，热量和动量几乎完全沿着（但不是穿过）磁场线传输。我们执行的第一个完全自洽的Braginskiii-MHD模拟的星系团，包括这两个影响。具体来说，我们进行局部和全球模拟的磁热不稳定性（MTI）和热通量驱动的浮力不稳定性（HBI）和评估粘度的影响，其饱和度和天体物理的影响。我们发现粘度对MTI的饱和度只有适度的影响。在以前的计算中，我们发现，MTI可以在星系团的外部产生近音速的湍流速度，虽然粘性有点抑制磁场放大。在冷核团簇的较小半径处，粘性可以降低HBI的线性增长率。然而，它对HBI的非线性饱和度的影响较小，部分原因是三维交换运动（磁通量管彼此滑过）不受各向异性粘性的阻尼。在冷核心集群的全球模拟中，我们表明，HBI强烈抑制径向热传导，从而沉淀冷却灾难。粘性的影响，然而，更重要的是更高的熵集群。我们认为粘性可以促进团核从冷核状态向非冷核状态的整体转变：另外的团内湍流源，如活动星系核反馈或星系尾流，通过热传导加热团核，抑制HBI;这使得ICM更粘稠，这减慢了HBI的生长，允许进一步传导加热簇芯并转变到非冷芯状态。

英文摘要：

In the intracluster medium (ICM) of galaxy clusters, heat and momentum are transported almost entirely along (but not across) magnetic field lines. We perform the first fully self-consistent Braginskii-MHD simulations of galaxy clusters including both of these effects. Specifically, we perform local and global simulations of the magnetothermal instability (MTI) and the heat-flux-driven buoyancy instability (HBI) and assess the effects of viscosity on their saturation and astrophysical implications. We find that viscosity has only a modest effect on the saturation of the MTI. As in previous calculations, we find that the MTI can generate nearly sonic turbulent velocities in the outer parts of galaxy clusters, although viscosity somewhat suppresses the magnetic field amplification. At smaller radii in cool-core clusters, viscosity can decrease the linear growth rates of the HBI. However, it has less of an effect on the HBI's nonlinear saturation, in part because three-dimensional interchange motions (magnetic flux tubes slipping past each other) are not damped by anisotropic viscosity. In global simulations of cool core clusters, we show that the HBI robustly inhibits radial thermal conduction and thus precipitates a cooling catastrophe. The effects of viscosity are, however, more important for higher entropy clusters. We argue that viscosity can contribute to the global transition of cluster cores from cool-core to non cool-core states: additional sources of intracluster turbulence, such as can be produced by AGN feedback or galactic wakes, suppress the HBI, heating the cluster core by thermal conduction; this makes the ICM more viscous, which slows the growth of the HBI, allowing further conductive heating of the cluster core and a transition to a non cool-core state.

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