Simulations of disk galaxies with cosmic ray driven galactic winds

TL;DR

This paper uses high-resolution hydrodynamic simulations to show that cosmic rays can effectively drive galactic winds with properties matching observations, differing significantly from supernova-driven winds.

Contribution

It introduces a novel model for cosmic ray feedback in galaxy simulations, demonstrating its ability to produce realistic wind properties and scaling relations.

Findings

CRs drive winds with high mass loading factors in dwarf galaxies.

CR-driven winds have different acceleration mechanisms compared to SN winds.

Winds contain significant warm gas, explaining observed halo gas.

Abstract

We present results from high-resolution hydrodynamic simulations of isolated SMC- and Milky Way-sized galaxies that include a model for feedback from galactic cosmic rays (CRs). We find that CRs are naturally able to drive winds with mass loading factors of up to ~10 in dwarf systems. The scaling of the mass loading factor with circular velocity between the two simulated systems is consistent with \propto v_c^{1-2} required to reproduce the faint end of the galaxy luminosity function. In addition, simulations with CR feedback reproduce both the normalization and the slope of the observed trend of wind velocity with galaxy circular velocity. We find that winds in simulations with CR feedback exhibit qualitatively different properties compared to SN driven winds, where most of the acceleration happens violently in situ near star forming sites. In contrast, the CR-driven winds are accelerated gently by the large-scale pressure gradient established by CRs diffusing from the star-forming galaxy disk out into the halo. The CR-driven winds also exhibit much cooler temperatures and, in the SMC-sized system, warm (T~10^4 K) gas dominates the outflow. The prevalence of warm gas in such outflows may provide a clue as to the origin of ubiquitous warm gas in the gaseous halos of galaxies detected via absorption lines in quasar spectra.