盘状星系形成的磁流体动力学模拟：冷热介质的磁化
Magnetohydrodynamic Simulations of Disk Galaxy Formation: the Magnetization of The Cold and Warm Medium
摘要：
利用磁流体动力学（MHD）自适应网格加密模拟方法，研究了具有磁化星际介质的盘星系的形成和早期演化。对于初始NFW暗物质和气体分布的$10^{10}$ \msun晕，我们施加一个均匀的$10^{-9}$ G磁场，并遵循其崩溃，磁盘的形成和演化到1 Gyr。与相同初始条件下的纯流体动力学模拟相比，我们发现这种强度的原星系场对全球盘的性质没有显著影响。同时，初始磁场被差动旋转的湍流盘快速放大。在持续$\sim500$ Myr的初始快速扩增之后，随后的场扩增似乎是自我调节的。因此，高度磁化的物质开始在磁盘的上方和下方形成。有趣的是，在自我调节制度的场强同意以及在银河系中观察到的领域都在温暖和寒冷的HI阶段，并不随时间而变化明显。大部分冷相显示出磁场强度的十阶色散。全球方位磁场在不同半径处反转，并且振幅作为盘半径的函数而下降。通过比较流体动力学模拟和MHD模拟的恒星形成率（SFR），我们发现在磁场强度饱和后，磁力在冷气体中提供了进一步的支持，导致SFR的下降。
英文摘要：
Using magnetohydrodynamic (MHD) adaptive mesh refinement simulations, we study the formation and early evolution of disk galaxies with a magnetized interstellar medium. For a $10^{10}$ \msun halo with initial NFW dark matter and gas profiles, we impose a uniform $10^{-9}$ G magnetic field and follow its collapse, disk formation and evolution up to 1 Gyr. Comparing to a purely hydrodynamic simulation with the same initial condition, we find that a protogalactic field of this strength does not significantly influence the global disk properties. At the same time, the initial magnetic fields are quickly amplified by the differentially rotating turbulent disk. After the initial rapid amplification lasting $\sim500$ Myr, subsequent field amplification appears self-regulated. As a result, highly magnetized material begin to form above and below the disk. Interestingly, the field strengths in the self-regulated regime agrees well with the observed fields in the Milky Way galaxy both in the warm and the cold HI phase and do not change appreciably with time. Most of the cold phase shows a dispersion of order ten in the magnetic field strength. The global azimuthal magnetic fields reverse at different radii and the amplitude declines as a function of radius of the disk. By comparing the estimated star formation rate (SFR) in hydrodynamic and MHD simulations, we find that after the magnetic field strength saturates, magnetic forces provide further support in the cold gas and lead to a decline of the SFR.
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