盘星系中各向同性和各向异性cosmic ray扩散驱动的星系风
Galactic winds driven by isotropic and anisotropic cosmic ray diffusion in disk galaxies
摘要：
宇宙射线（CR）物理学是解释星系风和外流驱动的一个有希望的候选者。最近的星系形成模拟表明，需要积极的CR运输无论是在扩散或流的形式，成功地在星系中发射风。然而，由于计算的限制，大多数以前的模拟模型CR输运各向同性。在这里，我们讨论了高分辨率模拟孤立盘星系的$10^{11}\rm{M_\odot}$晕与移动网格代码{ \sc Arepo}，包括注入的CR从超新星，平流运输，CR冷却，CR运输通过各向同性或各向异性扩散。我们发现，无论是扩散模式导致形成强双极外流。然而，与各向同性扩散的模拟相比，它们在各向异性扩散的模拟中显着较晚地发展。此外，我们发现，各向同性扩散允许大部分的CR迅速扩散出磁盘，而在模拟与各向异性扩散，大多数CR留在磁盘中，一旦磁场成为占主导地位的方位角分量，这发生在$\sim 300\,{\rm Myrs}$。这对圆盘中的气体动力学有重要的影响。特别是，我们表明，各向同性扩散强烈抑制放大的磁场的磁盘相比，各向异性或无扩散模型。因此，我们得出结论，可靠的模拟，其中包括CR运输不可避免地需要考虑各向异性扩散。
英文摘要：
The physics of cosmic rays (CR) is a promising candidate for explaining the driving of galactic winds and outflows. Recent galaxy formation simulations have demonstrated the need for active CR transport either in the form of diffusion or streaming to successfully launch winds in galaxies. However, due to computational limitations, most previous simulations have modeled CR transport isotropically. Here, we discuss high resolution simulations of isolated disk galaxies in a $10^{11}\rm{M_\odot}$ halo with the moving mesh code {\sc Arepo} that include injection of CRs from supernovae, advective transport, CR cooling, and CR transport through isotropic or anisotropic diffusion. We show that either mode of diffusion leads to the formation of strong bipolar outflows. However, they develop significantly later in the simulation with anisotropic diffusion compared to the simulation with isotropic diffusion. Moreover, we find that isotropic diffusion allows most of the CRs to quickly diffuse out of the disk, while in the simulation with anisotropic diffusion, most CRs remain in the disk once the magnetic field becomes dominated by its azimuthal component, which occurs after $\sim 300\,{\rm Myrs}$. This has important consequences for the gas dynamics in the disk. In particular, we show that isotropic diffusion strongly suppresses the amplification of the magnetic field in the disk compared to anisotropic or no diffusion models. We therefore conclude that reliable simulations which include CR transport inevitably need to account for anisotropic diffusion.
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