1304.6142 (Brian C. Lacki)

The Ultimate Fate of Cosmic Rays from Galaxies and their Role in the Intergalactic Medium    [PDF]

Brian C. Lacki

The majority of cosmic rays (CRs) generated by star-forming galaxies escape those galaxies and enter the intergalactic medium (IGM). I show that the mean pressure of the intergalactic CRs is likely 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 end up in, they are a significant contributor to its pressure support if its temperature is ~10^4 K, regardless of density. Which phase the CRs end up in depends on the structure and strength of intergalactic magnetic fields. I argue that CRs end up at least 100 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.

View original: http://arxiv.org/abs/1304.6142