Current-day cosmic ray (CR) propagation studies use static Milky Way models and fit parametrized source distributions to data. Instead, we use three-dimensional magnetohydrodynamic (MHD) simulations of isolated galaxies with the moving-mesh code arepo that self-consistently accounts for hydrodynamic effects of CR protons. In post-processing, we calculate their steady-state spectra, taking into account all relevant loss processes. We show that this steady-state assumption is well justified in the disc and generally for regions that emit non-thermal radio and gamma rays. Additionally, we model the spectra of primary electrons, accelerated by supernova remnants, and secondary electrons and positrons produced in hadronic CR proton interactions with the gas. We find that proton spectra above 10 GeV only weakly depend on galactic radius, while they acquire a radial dependence at lower energies due to Coulomb interactions. Radiative losses steepen the spectra of primary CR electrons in the central galactic regions, while diffusive losses dominate in the outskirts. Secondary electrons exhibit a steeper spectrum than primaries because they originate from the transported steeper CR proton spectra. Consistent with Voyager-1 and AMS-02 data, our models (i) show a turnover of proton spectra below GeV energies due to Coulomb interactions so that electrons start to dominate the total particle spectra and (ii) match the shape of the positron fraction up to 10 GeV. We conclude that our steady-state CR modelling in MHD CR galaxy simulations is sufficiently realistic to capture the dominant transport effects shaping their spectra, arguing for a full MHD treatment to accurately model CR transport in the future.

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模拟星系中的宇宙射线和非热发射 - I. 与 Voyager-1 数据相比的电子和质子光谱

当前的宇宙射线 (CR) 传播研究使用静态银河系模型，并将参数化的源分布拟合到数据中。相反，我们使用孤立星系的三维磁流体动力学 (MHD) 模拟，其移动网格代码 arepo 自洽地解释了 CR 质子的流体动力学效应。在后处理中，我们计算它们的稳态光谱，同时考虑所有相关的损失过程。我们表明，这种稳态假设在圆盘中是合理的，通常适用于发射非热射电和伽马射线的区域。此外，我们模拟了由超新星遗迹加速的初级电子，以及在强子 CR 质子与气体相互作用中产生的次级电子和正电子的光谱。我们发现高于 10 GeV 的质子光谱仅微弱地依赖于银河半径，而由于库仑相互作用，它们在较低能量下获得径向依赖性。辐射损失使中央星系区域的初级CR电子的光谱变陡，而扩散损失在外围占主导地位。二次电子表现出比一次电子更陡峭的光谱，因为它们源自传输的更陡峭的 CR 质子光谱。与 Voyager-1 和 AMS-02 数据一致，我们的模型 (i) 显示由于库仑相互作用导致质子光谱转换低于 GeV 能量，因此电子开始主导总粒子光谱和 (ii) 匹配正电子部分的形状高达 10 GeV。我们得出结论，我们在 MHD CR 星系模拟中的稳态 CR 建模足够逼真，可以捕捉塑造其光谱的主要传输效应，