We study the impact of cosmic rays (CRs) on the structure of virial shocks, using a large suite of high-resolution cosmological FIRE-2 simulations accounting for CR injection by supernovae. In Milky Way-mass, low-redshift (z ≲ 1−2) haloes, which are expected to form ‘hot haloes’ with slowly cooling gas in quasi-hydrostatic equilibrium (with a stable virial shock), our simulations without CRs do exhibit clear virial shocks. The cooler phase condensing out from inflows becomes pressure confined to overdense clumps, embedded in low-density, volume-filling hot gas with volume-weighted cooling time longer than inflow time. The gas thus transitions sharply from cool free-falling inflow, to hot and thermal-pressure supported at approximately the virial radius (≈Rvir), and the shock is quasi-spherical. With CRs, we previously argued that haloes in this particular mass and redshift range build up CR-pressure-dominated gaseous haloes. Here, we show that when CR pressure dominates over thermal pressure, there is no significant virial shock. Instead, inflowing gas is gradually decelerated by the CR pressure gradient and the gas is relatively subsonic out to and even beyond Rvir. Rapid cooling also maintains subvirial temperatures in the inflowing gas within ∼Rvir.

中文翻译：

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在宇宙射线主导的星系晕中抑制了维里冲击

我们使用一整套高分辨率宇宙学 FIRE-2 模拟来研究宇宙射线 (CR) 对维里冲击结构的影响，该模拟解释了超新星的 CR 注入。在银河系质量的低红移 (z ≲ 1−2) 晕中，预计会在准流体静力平衡（具有稳定的维里冲击）中缓慢冷却气体形成“热晕”，我们没有 CR 的模拟确实表现出明显的病毒冲击。从流入流出的较冷相变成压力限制在过密的团块中，嵌入低密度、体积填充的热气体中，体积加权冷却时间比流入时间长。因此，气体从冷的自由落体流入急剧转变为近似维里半径 (≈Rvir) 的热压和热压，并且激波是准球形的。使用 CR，我们之前认为，在这个特定质量和红移范围内的晕圈会形成以 CR 压力为主的气态晕圈。在这里，我们表明当 CR 压力超过热压力时，没有明显的维里冲击。相反，流入的气体被 CR 压力梯度逐渐减速，并且气体相对亚音速输出到甚至超过 Rvir。快速冷却还将流入气体中的亚维里温度保持在~Rvir 内。