Simulations of MHD Instabilities in Intracluster Medium Including Anisotropic Thermal Conduction
Simulations of MHD Instabilities in Intracluster Medium Including Anisotropic Thermal Conduction
复制标题
簇内介质中 MHD 不稳定性（包括各向异性热传导）的模拟
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发表时间：
2009
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通讯作者：
I. Parrish
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作者：
Tamara Bogdanovic;Christopher S. Reynolds;S. Balbus;I. Parrish
我们对星系团中的冷却核心进行了一系列模拟，以研究最近发现的热通量浮力不稳定性(HBI)对核心演化的影响。我们的模型遵循冷却星系团核心的三维磁流体动力学(MHD)，并捕捉到沿磁场方向的各向异性热传导的影响，但没有考虑星系团的宇宙学背景或AGN的存在。我们的模型团簇根据其最终的热力学状态可以分为三类：灾变崩塌核、等温核和由磁场初始构型决定其最终状态的中间群。模拟的星系团核心在时间尺度上呈现出向热崩塌的演化，与零传导情况相比延长了约2-10倍。HBI的主要作用是将场线重新定向为垂直于温度梯度。一旦磁场被包裹在核心周围的球面上，核心就与进一步的传导加热隔绝(有效热传导被抑制到斯皮策数值的1/100以下)，并继续坍塌。我们推测，在真实的星系团中，中心活动星系核和可能的合并分子扮演着“搅拌器”的角色，周期性地扰乱方位场结构，并允许热传导零星地加热核心。
We perform a suite of simulations of cooling cores in clusters of galaxies in order to investigate the effect of the recently discovered heat flux buoyancy instability (HBI) on the evolution of cores. Our models follow the 3-dimensional magnetohydrodynamics (MHD) of cooling cluster cores and capture the effects of anisotropic heat conduction along the lines of magnetic field, but do not account for the cosmological setting of clusters or the presence of AGN. Our model clusters can be divided into three groups according to their final thermodynamical state: catastrophically collapsing cores, isothermal cores, and an intermediate group whose final state is determined by the initial configuration of magnetic field. Modeled cores that are reminiscent of real cluster cores show evolution towards thermal collapse on a time scale which is prolonged by a factor of ~2-10 compared with the zero-conduction cases. The principal effect of the HBI is to re-orient field lines to be perpendicular to the temperature gradient. Once the field has been wrapped up onto spherical surfaces surrounding the core, the core is insulated from further conductive heating (with the effective thermal conduction suppressed to less than 1/100th of the Spitzer value) and proceeds to collapse. We speculate that, in real clusters, the central AGN and possibly mergers play the role of"stirrers,"periodically disrupting the azimuthal field structure and allowing thermal conduction to sporadically heat the core.