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Title: Cosmic-ray driven galactic winds from the warm interstellar medium

We study the properties of cosmic-ray (CR) driven galactic winds from the warm interstellar medium using idealized spherically symmetric time-dependent simulations. The key ingredients in the model are radiative cooling and CR-streaming-mediated heating of the gas. Cooling and CR heating balance near the base of the wind, but this equilibrium is thermally unstable, leading to a multiphase wind with large fluctuations in density and temperature. In most of our simulations, the heating eventually overwhelms cooling, leading to a rapid increase in temperature and a thermally driven wind; the exception to this is in galaxies with the shallowest potentials, which produce nearly isothermal $T \approx 10^4\,$ K winds driven by CR pressure. Many of the time-averaged wind solutions found here have a remarkable critical point structure, with two critical points. Scaled to real galaxies, we find mass outflow rates $\dot{M}$ somewhat larger than the observed star-formation rate in low-mass galaxies, and an approximately ‘energy-like’ scaling $\dot{M} \propto v_{\rm esc}^{-2}$. The winds accelerate slowly and reach asymptotic wind speeds of only ∼0.4vesc. The total wind power is $\sim 1~{{\ \rm per\ cent}}$ of the power from supernovae, suggesting inefficient preventive CR feedback for the physical conditions modelled here. We predict significant spatially extended emission and absorption lines from 104–105.5 K gas; this may correspond to extraplanar diffuse ionized gas seen in star-forming galaxies.

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Author(s) / Creator(s):
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Publisher / Repository:
Oxford University Press
Date Published:
Journal Name:
Monthly Notices of the Royal Astronomical Society
Page Range / eLocation ID:
p. 6374-6391
Medium: X
Sponsoring Org:
National Science Foundation
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