Hanasz Michał, Strong Andrew W, Girichidis Philipp
Institute of Astronomy, Nicolaus Copernicus University, ul. Grudziadzka 5, 87-100 Toruń, Poland.
Max-Planck-Institut für extraterrestrische Physik, 85748 Garching, Germany.
Living Rev Comput Astrophys. 2021;7(1):2. doi: 10.1007/s41115-021-00011-1. Epub 2021 Jul 26.
We review numerical methods for simulations of cosmic ray (CR) propagation on galactic and larger scales. We present the development of algorithms designed for phenomenological and self-consistent models of CR propagation in kinetic description based on numerical solutions of the Fokker-Planck equation. The phenomenological models assume a stationary structure of the galactic interstellar medium and incorporate diffusion of particles in physical and momentum space together with advection, spallation, production of secondaries and various radiation mechanisms. The self-consistent propagation models of CRs include the dynamical coupling of the CR population to the thermal plasma. The CR transport equation is discretized and solved numerically together with the set of MHD equations in various approaches treating the CR population as a separate relativistic fluid within the two-fluid approach or as a spectrally resolved population of particles evolving in physical and momentum space. The relevant processes incorporated in self-consistent models include advection, diffusion and streaming propagation as well as adiabatic compression and several radiative loss mechanisms. We discuss, applications of the numerical models for the interpretation of CR data collected by various instruments. We present example models of astrophysical processes influencing galactic evolution such as galactic winds, the amplification of large-scale magnetic fields and instabilities of the interstellar medium.
我们回顾了用于模拟宇宙射线（CR）在星系及更大尺度上传播的数值方法。我们展示了基于福克 - 普朗克方程数值解，为动力学描述中CR传播的唯象模型和自洽模型设计的算法发展。唯象模型假定星系星际介质具有稳态结构，并将粒子在物理空间和动量空间中的扩散与平流、散裂、次级粒子产生以及各种辐射机制结合起来。CR的自洽传播模型包括CR群体与热等离子体的动力学耦合。在各种方法中，将CR输运方程离散化并进行数值求解，同时将MHD方程组中的CR群体在双流体方法中视为单独的相对论流体，或者在物理空间和动量空间中视为按谱分辨的粒子群体进行演化。自洽模型中纳入的相关过程包括平流、扩散和流传播，以及绝热压缩和几种辐射损失机制。我们讨论了数值模型在解释各种仪器收集的CR数据方面的应用。我们展示了影响星系演化的天体物理过程的示例模型，如星系风、大尺度磁场的放大和星际介质的不稳定性。
