The physics of galactic winds driven by cosmic rays – II. Isothermal streaming solutions

ABSTRACT We use analytical calculations and time-dependent spherically symmetric simulations to study the properties of isothermal galactic winds driven by cosmic rays (CRs) streaming at Alfvén velocity. The produce flows permeated strong shocks; we identify a new linear instability sound waves that sources these shocks. shocks substantially modify wind dynamics, invalidating previous steady state models: CR pressure pc has staircase-like structure with dpc/dr ≃ 0 in most volume, time-averaged energetics are many cases better approximated ∝ ρ1/2, rather than canonical ρ2/3. Accounting for this change energetics, analytically derive expressions mass-loss rate, momentum flux, speed, kinetic power streaming. show CRs ineffective directly driving cold gas out galaxies, though CR-driven hotter ISM phases may entrain cool gas. For same physical conditions, diffusive transport (Paper I) yields rates few-100 times larger transport, asymptotic powers factor ≃4 larger. discuss implications our results theory observations; CR-streaming-induced instabilities wide range densities temperatures, consistent multiphase nature observed winds. also quantify applicability approximation modelling highlight need more realistic thermodynamics.