Magneto-thermal instability in galaxy clusters - II. three-dimensional simulations
Magneto-thermal instability in galaxy clusters - II. three-dimensional simulations
复制标题
星系团中的磁热不稳定性 - II。
DOI：
10.1093/mnras/stac975
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发表时间：
2022
影响因子：
4.8
通讯作者：
Perrone L
中科院分区：
文献类型：
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作者：
Perrone L
在星系的星系团内介质（ICM）中，磁场线之间的热量交换被强烈抑制。这种各向异性热传导，在存在大尺度温度梯度的情况下，通过磁热不稳定性（MTI）使星系团外围不稳定，这可能导致观测到的ICM湍流。在本文中，我们继续使用Boussinesq码谱对MTI进行三维模拟研究。我们纠正了两个固有的问题，我们以前的二维研究：一个逆能量级联和发电机作用的不可能性。与二维模拟相反，我们发现能量跨尺度的传输无关紧要（大多数能量在与其注入相同的尺度上耗散），湍流漩涡在热传导长度处或以下被垂直拉长，但在较大尺度上相对各向同性。然而，与二维相似，饱和湍流能级和积分尺度遵循明确的幂律，幂律取决于热扩散率、温度梯度和浮力频率。我们还发现，如果MTI湍流的积分尺度大于粘性耗散尺度，则MTI通过波动发电机将磁场放大到均分强度。最后，我们表明，如果热导率从其斯皮策值降低约10倍，我们的标度定律与现有的ICM湍流观测结果一致，并且稳定的分层显著降低了全球簇尺度上MTI运动的垂直延伸。
In the intracluster medium (ICM) of galaxies, exchanges of heat across magnetic field lines are strongly suppressed. This anisotropic heat conduction, in the presence of a large-scale temperature gradient, destabilizes the outskirts of galaxy clusters via the magneto-thermal instability (MTI), which could drive observed ICM turbulence. In this paper we continue our investigation of the MTI with 3D simulations using the Boussinesq codesnoopy. We redress two issues intrinsic to our previous 2D study: an inverse energy cascade and the impossibility of dynamo action. Contrary to 2D simulations, we find inconsequential transport of energy across scales (most energy is dissipated at the same scale as its injection) and that turbulent eddies are vertically elongated at or below the thermal conduction length yet relatively isotropic on larger scales. Similar to 2D, however, the saturated turbulent energy levels and the integral scale follow clear power-laws that depend on the thermal diffusivity, temperature gradient, and buoyancy frequency. We also show that the MTI amplifies magnetic fields, through a fluctuation dynamo, to equipartition strengths provided that the integral scale of MTI turbulence is larger than the viscous dissipation scale. Finally, we show that our scaling laws are consistent with extant observations of ICM turbulence if the thermal conductivity is reduced by a factor of ∼10 from its Spitzer value, and that the stable stratification significantly reduces the vertical elongation of MTI motions on global cluster scales.