On the amplification of magnetic fields in cosmic filaments and galaxy clusters
On the amplification of magnetic fields in cosmic filaments and galaxy clusters
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DOI：
10.1093/mnras/stu1896
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发表时间：
2014-09
影响因子：
4.8
通讯作者：
F. Vazza;M. Brüggen;C. Gheller;P. Wang
中科院分区：
文献类型：
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作者：
F. Vazza;M. Brüggen;C. Gheller;P. Wang
在结构形成过程中，原始磁场通过小尺度湍流发电机的放大可能能够解释星系团中观测到的磁场。更纤细的大尺度结构（如宇宙细丝）的磁化强度更不确定，因为数值模拟实现所需的动态范围具有挑战性。在这项工作中，我们提出了磁流体动力学的宇宙学模拟大均匀网格上的原始种子场的放大研究在集群内介质（ICM）和在温暖的热星系际介质（WHIM）。在ICM中，我们证实，结构形成引起的湍流可以产生显着的发电机放大，即使放大比其他论文中报道的要小。在WHIM内细丝，我们没有观察到显着的发电机放大，即使我们实现了雷诺数的$R_{\rm e} \sim 200-300$。对于大的细丝的最大放大是$\sim 100$的数量级的磁能，对应于一个典型的几个$\sim \rm nG$从一个$10^{-10}$ G的原始弱场（共动）。为了启动一个小规模的发电机，我们发现，在星系团的维里半径范围内，至少需要10^2$分辨率的元素。在细丝中，我们找不到启动发电机的最小分辨率。这是由于WHIM中的超音速运动在触发螺线管模式和磁场结构的小尺度扭曲方面效率低下。如此小的磁场将使得在射电观测中很难检测到细丝。
The amplification of primordial magnetic fields via a small-scale turbulent dynamo during structure formation might be able to explain the observed magnetic fields in galaxy clusters. The magnetisation of more tenuous large-scale structures such as cosmic filaments is more uncertain, as it is challenging for numerical simulations to achieve the required dynamical range. In this work, we present magneto-hydrodynamical cosmological simulations on large uniform grids to study the amplification of primordial seed fields in the intracluster medium (ICM) and in the warm-hot-intergalactic medium (WHIM). In the ICM, we confirm that turbulence caused by structure formation can produce a significant dynamo amplification, even if the amplification is smaller than what is reported in other papers. In the WHIM inside filaments, we do not observe significant dynamo amplification, even though we achieve Reynolds numbers of $R_{\rm e} \sim 200-300$. The maximal amplification for large filaments is of the order of $\sim 100$ for the magnetic energy, corresponding to a typical field of a few $\sim \rm nG$ starting from a primordial weak field of $10^{-10}$ G (comoving). In order to start a small-scale dynamo, we found that a minimum of $\sim 10^2$ resolution elements across the virial radius of galaxy clusters was necessary. In filaments we could not find a minimum resolution to set off a dynamo. This stems from the inefficiency of supersonic motions in the WHIM in triggering solenoidal modes and small-scale twisting of magnetic field structures. Magnetic fields this small will make it hard to detect filaments in radio observations.