Can supernova from runaway stars mimic the signs of absorbing `super-virial' gas?

Abstract

The recent detection of large column density absorption lines from highly ionized gas in a few directions through the circumgalactic medium (CGM) of the Milky Way (MW) has been puzzling. The inferred temperature from these absorption lines far exceeds the virial temperature of the MW, and the column densities are also too large to be easily explained. In this paper, we propose a novel idea to explain these observations and claim that they may not have originated from the CGM, but from a totally different type of source, namely, stellar ejecta from supernovae (SNe) above the Galactic disk that happen to lie in the line of sight to the background quasars. About $\sim 20\%$ of massive OB stars (progenitors of core-collapse supernovae) are known to be runaway stars that have high ejection velocities near the Galactic plane and can end up exploding as SNe above the Galactic disk. We show that the associated reverse shock in the supernova remnant in the early non-radiative phase can heat the ejecta to temperatures of $\gtrsim 10^7\mathrm{K}$ and can naturally explain the observed high column density of ions in the observed `super-virial' phase along with $\alpha$-enriched super-solar abundance that is typical of core-collapse supernovae. However, SNe from runaway stars has a covering fraction of $\lesssim 0.7\%$ and thus can only explain the observations along limited sightlines.

14 pages, accepted for publication in the Astrophysical Journal (ApJ)

References in corpus (15)

• galpy: A Python Library for Galactic Dynamics
• The Circumgalactic Medium
• The mass distribution and gravitational potential of the Milky Way
• Nucleosynthesis and Remnants in Massive Stars of Solar Metallicity
• Abundance and temperature of the outer hot circum-Galactic medium: The SRG/eROSITA view of the soft X-ray background in the eFEDS field
• The hot circumgalactic medium of the Milky Way: evidence for super-virial, virial, and sub-virial temperature, non-solar chemical composition, and non-thermal line broadening
• Super-virial temperature or Neon overabundance?: Suzaku observations of the Milky Way circumgalactic Medium
• A Statistical Analysis of Galactic Radio Supernova Remnants
• Unveiling the nature of the unidentified gamma-ray sources VI: gamma-ray blazar candidates in the WISH survey and their radio properties
• Widespread Detection of Two Components in the Hot Circumgalactic Medium of the Milky Way
• A feather on the hat: Tracing the giant stellar stream around the Sombrero galaxy
• The hot circumgalactic medium of the Milky-Way: new insights from XMM-Newton observations
• Detection of a Super-Virial Hot Component in the Milky Way Circumgalactic Medium Along Multiple Sight-Lines by Using the Stacking Technique
• A Sub-solar Fe/O, logT~7.5 Gas Component Permeating the Milky Way's CGM
• On Stellar Migration from Andromeda to the Milky Way

Cited by in corpus (1)

• Supernova explosions of runaway stars and young neutron stars above the Galactic plane