标题： 螺旋星系中因全球速度场而产生的磁场结构 显示英文标题

标题： Magnetic field structure due to the global velocity field in spiral galaxies

摘要： 我们展示了一组全局的、自洽的N体/光滑粒子流体（SPH）模拟，用于研究包含气体和磁场的星系盘的动力学演化。 我们在Vine代码的SPH部分实现了理想磁感应方程来描述磁场的演化。 通过直接实现场方程得到的结果与由欧拉势表示的结果进行了比较，后者提供了一个无div(B)的描述，并且这种约束在直接实现中未被满足。 所有模拟均与Gadget代码中包含磁场的实现进行了比较，后者还包括用于消除div(B)的方法。 从均匀种子磁场开始，我们发现通过盘的差动旋转和螺旋结构形成，磁场在盘的五个旋转周期内放大了一个数量级。 数值分辨率越高，放大效果越强。 此外，我们发现在我们的模拟中，磁场结构与星系的密度模式紧密相连，磁场线与气体形成的螺旋图案对齐。 我们的模拟明确显示了非轴对称性对于磁场演化的重要性。 显示英文摘要

摘要： We present a set of global, self-consistent N-body/SPH simulations of the dynamic evolution of galactic discs with gas and including magnetic fields. We have implemented a description to follow the evolution of magnetic fields with the ideal induction equation in the SPH part of the Vine code. Results from a direct implementation of the field equations are compared to a representation by Euler potentials, which pose a div(B)-free description, an constraint not fulfilled for the direct implementation. All simulations are compared to an implementation of magnetic fields in the Gadget code which includes also cleaning methods for div(B). Starting with a homogeneous seed field we find that by differential rotation and spiral structure formation of the disc the field is amplified by one order of magnitude within five rotation periods of the disc. The amplification is stronger for higher numerical resolution. Moreover, we find a tight connection of the magnetic field structure to the density pattern of the galaxy in our simulations, with the magnetic field lines being aligned with the developing spiral pattern of the gas. Our simulations clearly show the importance of non-axisymmetry for the evolution of the magnetic field.