Impact of supernova and cosmic-ray driving on the surface brightness of the galactic halo in soft X-rays

Abstract

The halo of the Milky Way contains a hot plasma with a surface brightness in soft X-rays of the order $10^{-12}$erg cm${}^{-2}$ s${}^{-1}$ deg${}^{-2}$. The origin of this gas is unclear, but so far numerical models of galactic star formation have failed to reproduce such a large surface brightness by several orders of magnitude. In this paper, we analyze simulations of the turbulent, magnetized, multi-phase interstellar medium including thermal feedback by supernova explosions as well as cosmic-ray feedback. We include a time-dependent chemical network, self-shielding by gas and dust, and self-gravity. Pure thermal feedback alone is sufficient to produce the observed surface brightness, although it is very sensitive to the supernova rate. Cosmic rays suppress this sensitivity and reduce the surface brightness because they drive cooler outflows. Self-gravity has by far the largest effect because it accumulates the diffuse gas in the disk in dense clumps and filaments, so that supernovae exploding in voids can eject a large amount of hot gas into the halo. This can boost the surface brightness by several orders of magnitude. Although our simulations do not reach a steady state, all simulations produce surface brightness values of the same order of magnitude as the observations, with the exact value depending sensitively on the simulation parameters. We conclude that star formation feedback alone is sufficient to explain the origin of the hot halo gas, but measurements of the surface brightness alone do not provide useful diagnostics for the study of galactic star formation.

ApJ Letters in press

References in corpus (9)

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Cited by in corpus (22)

• The SILCC project: III. Regulation of star formation and outflows by stellar winds and supernovae
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• Global simulations of galactic winds including cosmic ray streaming
• Cooler and smoother -- the impact of cosmic rays on the phase structure of galactic outflows
• The role of cosmic ray pressure in accelerating galactic outflows
• Impact of Cosmic Ray Transport on Galactic Winds
• Quantifying Supernovae-Driven Multiphase Galactic Outflows
• The SILCC project --- IV. Impact of dissociating and ionising radiation on the interstellar medium and Halpha emission as a tracer of the star formation rate
• Cosmic ray driven Galactic winds
• Cosmic-Ray Diffusion Suppression in Star-forming Regions Inhibits Clump Formation in Gas-rich Galaxies
• How Do Supernovae Impact the Circumgalactic Medium? I. Large-Scale Fountains Around a Milky Way-Like Galaxy
• Synthetic observations of star formation and the interstellar medium
• Simulations of cosmic ray propagation
• The SATIN project I: Turbulent multi-phase ISM in Milky Way simulations with SNe feedback from stellar clusters
• Cosmic Rays in a Galactic Breeze
• The turbulent life of dust grains in the supernova-driven, multi-phase interstellar medium
• Cosmic Ray-Driven Galactic Winds with Resolved ISM and Ion-Neutral Damping
• Selected Topics in Cosmic Ray Physics
• Tracing the Origins of Hot Halo Gas in Milky Way-Type Galaxies with SMUGGLE
• Galactic Cosmic-Rays in a Breeze
• Galactic chimney sweeping: the effect of 'gradual' stellar feedback mechanisms on the evolution of dwarf galaxies
• Outflows from starburst galaxies with various driving mechanisms and their X-ray properties