We study the effects of cosmic rays (CRs) on outflows from star-forming galaxies in the circum and inter-galactic medium (CGM/IGM), in high-resolution, fully-cosmological FIRE-2 simulations (accounting for mechanical and radiative stellar feedback, magnetic fields, anisotropic conduction/viscosity/CR diffusion and streaming, and CR losses). We showed previously that massive ($M_{\rm halo}\gtrsim 10^{11}\,M_{\odot}$), low-redshift ($z\lesssim 1-2$) halos can have CR pressure dominate over thermal CGM pressure and balance gravity, giving rise to a cooler CGM with an equilibrium density profile. This dramatically alters outflows. Absent CRs, high gas thermal pressure in massive halos "traps" galactic outflows near the disk, so they recycle. With CRs injected in supernovae as modeled here, the low-pressure halo allows "escape" and CR pressure gradients continuously accelerate this material well into the IGM in "fast" outflows, while lower-density gas at large radii is accelerated in-situ into "slow" outflows that extend to $>$Mpc scales. CGM/IGM outflow morphologies are radically altered: they become mostly volume-filling (with inflow in a thin mid-plane layer) and coherently biconical from the disk to $>$Mpc. The CR-driven outflows are primarily cool ($T\sim10^{5}\,$K) and low-velocity. All of these effects weaken and eventually vanish at lower halo masses ($\lesssim 10^{11}\,M_{\odot}$) or higher redshifts ($z\gtrsim 1-2$), reflecting the ratio of CR to thermal+gravitational pressure in the outer halo. We present a simple analytic model which explains all of the above phenomena.

中文翻译：

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宇宙射线驱动从 L* 星系流出到 Mpc 尺度

我们在高分辨率、全宇宙学 FIRE-2 模拟（考虑机械和辐射恒星）中研究宇宙射线 (CRs) 对周围和星系间介质 (CGM/IGM) 中恒星形成星系外流的影响。反馈、磁场、各向异性传导/粘度/CR 扩散和流动，以及 CR 损失）。我们之前表明，巨大的 ($M_{\rm halo}\gtrsim 10^{11}\,M_{\odot}$)、低红移 ($z\lesssim 1-2$) 晕可以使 CR 压力支配热 CGM 压力和平衡重力，产生具有平衡密度分布的较冷 CGM。这极大地改变了流出量。如果没有 CR，大量晕中的高气体热压会“捕获”盘附近的星系外流，因此它们会循环使用。在此处模拟的超新星中注入 CR 后，低压晕允许“逃逸” 和 CR 压力梯度不断加速这种物质以“快速”流出进入 IGM，而大半径的低密度气体在原位加速进入“缓慢”流出，扩展到 $>$Mpc 规模。CGM/IGM 流出形态发生了根本性的改变：它们主要是体积填充（流入薄的中间平面层）并且从圆盘到 $>$Mpc 的连贯双锥形。CR 驱动的流出主要是凉爽的 ($T\sim10^{5}\,$K) 和低速。所有这些影响都会减弱并最终在较低的晕质量（$\lesssim 10^{11}\,M_{\odot}$）或更高的红移（$z\gtrsim 1-2$）下消失，反映了 CR 与外晕中的热+重力压力。我们提出了一个简单的分析模型来解释上述所有现象。