Cosmic ray driven outflows from high redshift galaxies
  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 NFW form, relevant to galaxies. Cosmic rays naturally provide
the extra energy and/or momentum input to the system, needed for a transonic
wind solution in a gas with adiabatic index $\gamma=5/3$. 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 (eta_w) is predicted to be ~ 0.2-0.5
for massive galaxies, with masses $M \sim 10^{11}-10^{12} M_\odot$. We show
eta_w to be inversely proportional to the square of the circular velocity.
Magnetic fields at the $\mu$G levels are also required in these galaxies to
have a significant mass loss. A large eta_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 IGM. These conclusions are
applicable to the class of free wind models where the source region is confined
to be within the sonic point.
