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arXiv 1909.01280astro-ph.GAastro-ph.HE
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随时间变化的星系风

Time-dependent galactic winds

E. A. Dorfi, D. Steiner, F. Ragossnig, D. Breitschwerdt

摘要:

宇宙射线(CR)通过沿磁场线的扩散和平流以及自激磁流体动力学(MHD)波的共振散射被输送出星系。因此,动量通过冻结的波传递到等离子体,作为一种媒介,帮助驱动银河风的热压。星系CRs(GCRs)被超新星遗迹(SNRs)中产生的冲击波加速,并从圆盘传播到晕中。因此,在晕中的CR加速度强烈地依赖于内盘边界条件。我们进行了流体动力学模拟的星系风的通量管几何形状适合盘星系,描述CR扩散平流运输的流体动力学的方式(通过采取适当的时刻的福克-普朗克方程),以及与自生MHD波的能量交换。我们的时间相关的CR流体动力学模拟证实,反馈的星系风的演化依赖于星系晕的结构。在风结构晕的情况下,风在最后一颗超新星(SN)爆炸后分解。这里描述的机制提供了一个自然和优雅的解决方案来解释CR的幂律分布之间的“膝盖”和“脚踝”。这种过渡自然是平滑的,因为在SN激波处加速的银河CRs将被内边界处产生的激波和穿过晕的激波“后加速”。

英文摘要:

Cosmic rays (CRs) are transported out of the galaxy by diffusion and advection due to streaming along magnetic field lines and resonant scattering off self-excited Magneto-Hydro-Dynamic (MHD) waves. Thus momentum is transferred to the plasma via the frozen-in waves as a mediator assisting the thermal pressure in driving a galactic wind. Galactic CRs (GCRs) are accelerated by shock waves generated in supernova remnants (SNRs), and they propagate from the disc into the halo. Therefore CR acceleration in the halo strongly depends on the inner disc boundary conditions. We performed hydrodynamical simulations of galactic winds in flux tube geometry appropriate for disc galaxies, describing the CR diffusive-advective transport in a hydrodynamical fashion (by taking appropriate moments of the Fokker-Planck equation) along with the energy exchange with self-generated MHD waves. Our time-dependent CR hydrodynamic simulations confirm that the evolution of galactic winds with feedback depends on the structure of the galactic halo. In case of a wind-structured halo, the wind breaks down after the last super nova (SN) has exploded. The mechanism described here offers a natural and elegant solution to explain the power-law distribution of CRs between the `knee' and the `ankle'. The transition will be naturally smooth, because the Galactic CRs accelerated at SN shocks will be `post-accelerated' by shocks generated at the inner boundary and travelling through the halo.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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