Cosmic-Ray Driven Outflows to Mpc Scales from $L_{\ast}$ Galaxies
  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.
