The Ultimate Fate of Cosmic Rays from Galaxies and their Role in the
  Intergalactic Medium
  The majority of cosmic rays (CRs) generated by star-forming galaxies escape
them and enter the intergalactic medium (IGM). Galactic wind termination shocks
might also accelerate CRs. I show that the mean pressure of these CRs can reach
to within an order of magnitude of the mean Lyman-alpha forest thermal
pressure. At z >~ 1, their pressure may have even been dominant. I also
demonstrate that, whichever IGM phase the CRs reside in, they contribute
significantly to its pressure if its temperature is ~$10^4$ K, as long as
pionic and Coulomb losses are negligible. Where CRs end up depends on the
structure and strength of intergalactic magnetic fields. I argue that CRs end
up at least 30 kpc from their progenitor galaxies. CRs may self-confine in the
IGM to the sound speed, generating >~ $10^{-13}$ G magnetic fields. These
considerations imply the existence and importance of a nonthermal IGM.
