Cosmic ray driven outflows from high-redshift galaxies

Abstract

We study winds in high-redshift galaxies driven by a relativistic cosmic ray (proton) component in addition to the hot thermal gas component. Cosmic rays (CRs) are likely to be efficiently generated in supernova shocks inside galaxies. We obtain solutions of such CR-driven free winds in a gravitational potential of the Navarro-Frenk-White form, relevant to galaxies. CRs naturally provide the extra energy and/or momentum input to the system, needed for a transonic wind solution in a gas with adiabatic index γ = 5/3. We show that CRs can effectively drive winds even when the thermal energy of the gas is lost due to radiative cooling. These wind solutions predict an asymptotic wind speed closely related to the circular velocity of the galaxy. Furthermore, the mass outflow rate per unit star formation rate (η w ) is predicted to be ∼0.2-0.5 for massive galaxies, with masses M ∼ 10 11 -10 12 M . We show η w to be inversely proportional to the square of the circular velocity. Magnetic fields at the μG levels are also required in these galaxies to have a significant mass loss. A large η w for small mass galaxies implies that CR-driven outflows could provide a strong negative feedback to the star formation in dwarf galaxies. Further, our results will also have important implications to the metal enrichment of the intergalactic medium. These conclusions are applicable to the class of free wind models where the source region is confined to be within the sonic point.

Self-consistent Modeling of Reionization in Cosmological Hydrodynamical Simulations

“…This will allow us to better test the effect of such models in simulations of galaxy formation and the IGM. These models could include Population III stars (Manrique et al 2015), X-ray pre-heating coming from from starburst galaxies, supernova remnants, or miniquasars (Oh 2001;Glover & Brand 2003;Madau et al 2004;Furlanetto 2006), dark matter annihilation or decay (Liu et al 2016) or cosmic rays (Samui et al 2005), from the intergalactic absorption of blazar TeV photons Puchwein et al 2012), or from broadband intergalactic dust absorption (Inoue & Kamaya 2008). We expect more detailed studies on these physically motivated models in the future.…”

The ultimate fate of cosmic rays from galaxies and their role in the intergalactic medium

“…This population has been largely ignored. Nath & Biermann (1993) and Samui, Subramanian, & Srianand (2005) studied how CRs from SFGs could have reionized the IGM, or heated it at high redshift. But the pionic energy loss time for CRs with kinetic energies > ∼ GeV is ∼ 200 δ −1 Tyr, so energy injection is negligible in the rarefied IGM (Mannheim & Schlickeiser 1994;Schlickeiser 2002, hereafter S02).…”

Do cosmic rays heat the early intergalactic medium?

“…As they propagate in the IGM, CRs interact with the surrounding environments mainly via H/He photoionization and Coulomb collisions with free electrons, and by doing so they deposit thermal energy in the gas. Both mechanisms imply that CRs could contribute to the thermal history of the IGM (Samui et al 2005).…”