The small-scale dynamo and the amplification of magnetic fields in massive primordial haloes
The small-scale dynamo and the amplification of magnetic fields in massive primordial haloes
复制标题
大型原始晕中的小型发电机和磁场放大
DOI：
10.1093/mnras/stt503
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发表时间：
2013
影响因子：
4.8
通讯作者：
Niemeyer
中科院分区：
文献类型：
--
作者：
Schleicher;D. R. G;Schmidt;Niemeyer
虽然目前的标准宇宙学模型没有给出初始磁场强度的明确预测，但有效的发电机作用可以通过快速放大来补偿最初较弱的种子场。特别值得一提的是，这台小型发电机预计会在湍流存在的情况下以指数级放大任何弱磁场。我们使用模拟第一批星系形成的宇宙学磁流体力学模拟来探索这一场景是否可行，这些星系预计将在具有维里温度的所谓原子冷却晕Tvir≥104K中形成。由于以前的计算表明，需要高的牛仔裤分辨率来解决湍流结构和发电机效应，我们的计算使用了高达128个单元每牛仔裤长度的分辨率。发电机的存在可以清楚地证实，每牛仔裤长度至少有单元的分辨率，而饱和发生在与湍流能量近似等分的位置。由于原始星系的雷诺数很大，我们预计饱和将在早期阶段发生，这意味着在104厘米∼3密度下的磁场强度为0.1μG。
While the present standard model of cosmology yields no clear prediction for the initial magnetic field strength, efficient dynamo action may compensate for initially weak seed fields via rapid amplification. In particular, the small-scale dynamo is expected to exponentially amplify any weak magnetic field in the presence of turbulence. We explore whether this scenario is viable using cosmological magneto-hydrodynamics simulations modelling the formation of the first galaxies, which are expected to form in so-called atomic cooling haloes with virial temperaturesTvir≥ 104K. As previous calculations have shown that a high Jeans resolution is needed to resolve turbulent structures and dynamo effects, our calculations employ resolutions of up to 128 cells per Jeans length. The presence of the dynamo can be clearly confirmed for resolutions of at least 64 cells per Jeans length, while saturation occurs at approximate equipartition with turbulent energy. As a result of the large Reynolds numbers in primordial galaxies, we expect saturation to occur at early stages, implying magnetic field strengths of ∼0.1 μG at densities of 104cm−3.