SHAKEN AND STIRRED: CONDUCTION AND TURBULENCE IN CLUSTERS OF GALAXIES
SHAKEN AND STIRRED: CONDUCTION AND TURBULENCE IN CLUSTERS OF GALAXIES
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震动和搅动：星系团中的传导和湍流
DOI：
10.1088/0004-637x/713/2/1332
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发表时间：
2009
期刊：
影响因子：
--
通讯作者：
S. P. Oh
中科院分区：
文献类型：
--
作者：
M. Ruszkowski;M. Ruszkowski;S. P. Oh;S. P. Oh
星系团中不受抑制的辐射冷却将导致与观测相反的过高的质量吸积率。抵消辐射能量损失的关键建议之一是从冷核（CC）团簇的外部较热层到其中心的热传导。然而，热传导对磁场拓扑结构很敏感。在温度向内降低的CC团簇中，热浮力不稳定性（HBI）导致磁场优先排列在垂直于重力方向，这显著降低了传导性水平，低于经典的Spitzer-Braginskii值。然而，CC簇很少处于完美的流体静力平衡状态。由于轻微合并引起的晃动运动和由星系团或活动星系核引起的搅拌运动可以显著地扰乱气体。然后，湍流级联可以影响磁场的拓扑结构和热传导的有效水平。我们进行了三维自适应网格细化磁流体动力学模拟，模拟了湍流对CC团簇中各向异性热传导特性的影响。我们表明，在观测约束下，非常弱的亚音速运动可以使磁场随机化，并显着提高有效热传导，超出纯无扰动HBI情况下预期的饱和值。我们发现湍流运动基本上可以将CC的传导热流恢复到与高度纠缠场的理论最大值~ 1/3斯皮策相当的水平。采用辐射冷却的运行表明，可以避免冷却灾难，稳定堆芯；然而，这一结论可能取决于中心气体密度。在临界弗劳德数以上，这些相同的湍流运动也消除了速度和磁场中的切向偏置，否则由捕获的g模式引起，并可能允许显著的湍流热扩散。我们的结果可以用未来的无线电偏振测量来测试，并对金属在星系团中的有效扩散有影响。
Uninhibited radiative cooling in clusters of galaxies would lead to excessive mass accretion rates contrary to observations. One of the key proposals to offset radiative energy losses is thermal conduction from outer, hotter layers of cool core (CC) clusters to their centers. However, thermal conduction is sensitive to magnetic field topology. In CC clusters where temperature decreases inwards, the heat buoyancy instability (HBI) leads to magnetic fields ordered preferentially in the direction perpendicular to that of gravity, which significantly reduces the level of conduction below the classical Spitzer–Braginskii value. However, the CC clusters are rarely in perfect hydrostatic equilibrium. Sloshing motions due to minor mergers and stirring motions induced by cluster galaxies or active galactic nuclei can significantly perturb the gas. The turbulent cascade can then affect the topology of the magnetic field and the effective level of thermal conduction. We perform three-dimensional adaptive mesh refinement magnetohydrodynamical simulations of the effect of turbulence on the properties of the anisotropic thermal conduction in CC clusters. We show that very weak subsonic motions, well within observational constraints, can randomize the magnetic field and significantly boost effective thermal conduction beyond the saturated values expected in the pure unperturbed HBI case. We find that the turbulent motions can essentially restore the conductive heat flow to the CC to level comparable to the theoretical maximum of ∼1/3 Spitzer for a highly tangled field. Runs with radiative cooling show that the cooling catastrophe can be averted and the cluster core stabilized; however, this conclusion may depend on the central gas density. Above a critical Froude number, these same turbulent motions also eliminate the tangential bias in the velocity and magnetic field that is otherwise induced by the trapped g-modes, and possibly allow significant turbulent heat diffusion. Our results can be tested with future radio polarization measurements and have implications for efficient metal dispersal in clusters.
星系团中活动星系核的自我调节
DOI：
10.1111/j.1365-2966.2009.15216.x
发表时间：
2009
影响因子：
4.8
作者：
Brüggen M;Scannapieco E.
通讯作者：
Scannapieco E.