Simulations of magnetic fields in isolated disc galaxies
Simulations of magnetic fields in isolated disc galaxies
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DOI：
10.1093/mnras/stt428
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发表时间：
2012-12
影响因子：
4.8
通讯作者：
R. Pakmor;V. Springel
中科院分区：
文献类型：
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作者：
R. Pakmor;V. Springel
众所周知，磁场在我们银河系的星际介质中是动态重要的，它们在星系和星系团的光晕中的扩散气体中无处不在地被观察到。然而，在星系形成的研究中，磁场通常被忽略了，这使得它们对星系形成的全球影响基本上是不清楚的。我们将移动网格程序AREPO中的MHD实现扩展到包括辐射冷却和恒星形成在内的宇宙学问题。特别是，我们用Powell 8波方案取代了以前使用的发散清理方法，事实证明，即使在非常动态的环境中，它也要稳定得多。我们通过模拟吸积盘中的MRI来验证改进的准确性，该模拟再现了其正确的线性增长率。使用这个新的MHD程序，我们模拟了在有磁场和没有磁场的情况下，类似于银河系的孤立盘星系的形成。我们发现，在最初的恒星暴增和形成盘的差动旋转中，磁场被迅速放大，直到它最终饱和，当它变得与热压相当时。与没有磁场的模拟相比，附加压力分量导致较晚的恒星形成速率较低，并导致气盘螺旋臂结构的变化。此外，我们还观察到高度磁化的喷泉状流出。这些结果在数值分辨率上是稳健的，并且在很大程度上与初始条件中假定的初始磁场无关，因为放大过程是快速的和自我调节的。我们的发现表明了磁场对星系形成和演化的重要影响，告诫人们不要在结构形成的理论模型中忽视它们。
Magnetic fields are known to be dynamically important in the interstellar medium of our own Galaxy, and they are ubiquitously observed in diffuse gas in the halos of galaxies and galaxy clusters. Yet, magnetic fields have typically been neglected in studies of the formation of galaxies, leaving their global influence on galaxy formation largely unclear. We extend our MHD implementation in the moving-mesh code Arepo to cosmological problems which include radiative cooling and the formation of stars. In particular, we replace our previously employed divergence cleaning approach with a Powell 8-wave scheme, which turns out to be significantly more stable, even in very dynamic environments. We verify the improved accuracy through simulations of the MRI in accretion disks, that reproduce its correct linear growth rate. Using this new MHD code, we simulate the formation of isolated disk galaxies similar to the Milky Way using idealized initial conditions with and without magnetic fields. We find that the magnetic field is quickly amplified in the initial starburst and the differential rotation of the forming disk until it eventually saturates when it becomes comparable to the thermal pressure. The additional pressure component leads to a lower star formation rate at late times compared to simulations without magnetic fields, and induces changes in the spiral arm structures of the gas disk. In addition, we observe highly magnetized fountain-like outflows from the disk. These results are robust with numerical resolution and are largely independent of the initial magnetic seed field assumed in the initial conditions, as the amplification process is rapid and self-regulated. Our findings suggest an important influence of magnetic fields on galaxy formation and evolution, cautioning against their neglect in theoretical models of structure formation.