Turbulent magnetic fields in merging clusters: a case study of Abell 2146
Turbulent magnetic fields in merging clusters: a case study of Abell 2146
复制标题
合并星团中的湍流磁场：阿贝尔 2146 的案例研究
DOI：
10.1093/mnras/stac594
复制
发表时间：
2022
影响因子：
4.8
通讯作者：
Chadayammuri U
中科院分区：
文献类型：
--
作者：
Chadayammuri U
沿着星系团中接触不连续性的开尔文-亥姆霍兹不稳定性（KHI）已被用来约束星系团中的磁场强度，假设当磁场线围绕冷相和热相之间的界面时，它们的磁张力会抵抗扰动的增长。在模拟刚性物体穿过磁化介质和晃动的星系团时观察到了这一点，然后应用于解释合并冷锋的观测结果。使用一套双星团合并的磁流体动力学 (MHD) 模拟，我们发现即使磁场强度比观测到的强 (β =Pth/PB= 50)，也显示出可见的 KHI 特征。这是因为我们的初始磁场是纠缠的，在簇内介质（ICM）中产生阿尔文波和相关的速度波动；因此，更强的初始磁场会产生更大的波动，因此即使由于磁张力而降低的增长率也会产生显着的 KHI。最终结果是，更强的初始磁场会导致表面亮度和温度产生更剧烈的波动，而不是相反。我们表明，这很难与相同初始强度的湍流扰动的演化区分开来。因此，为了利用 ICM 中的 KHI 观测结果通过与理想化模拟进行比较来推断磁场强度，必须充分理解并（如果可能）仔细控制产生 KHI 的扰动。
Kelvin–Helmholtz instabilities (KHI) along contact discontinuities in galaxy clusters have been used to constrain the strength of magnetic fields in galaxy clusters, following the assumption that, as magnetic field lines drape around the interface between the cold and hot phases, their magnetic tension resists the growth of perturbations. This has been observed in simulations of rigid objects moving through magnetized media and sloshing galaxy clusters, and then applied in interpreting observations of merger cold fronts. Using a suite of magnetohydrodynamic (MHD) simulations of binary cluster mergers, we show that even magnetic field strengths stronger than yet observed (β =Pth/PB= 50) show visible KHI features. This is because our initial magnetic field is tangled, producing Alfvén waves and associated velocity fluctuations in the intracluster medium (ICM); stronger initial fields therefore seed larger fluctuations, so that even a reduced growth rate due to magnetic tension produces a significant KHI. The net result is that a stronger initial magnetic field produces more dramatic fluctuations in surface brightness and temperature, not the other way around. We show that this is hard to distinguish from the evolution of turbulent perturbations of the same initial magnitude. Therefore, in order to use observations of KHI in the ICM to infer magnetic field strengths by comparing to idealized simulations, the perturbations that seed the KHI must be well understood and (if possible) carefully controlled.