Diagnostics of Gaseous Halo of the Milky Way by a Shock Wave from the Galactic Centre

Abstract

A method to diagnose the gas distribution in the Galactic halo using a shock wave from the Galactic Centre (GC) is presented. Propagation of a shock wave caused by central explosion with released energy $\sim 10^{55}$ erg is calculated for various models of the gaseous halo, and the shock front morphology is compared with the observed North- (NPS) and South-Polar Spurs (SPS). The observed bipolar hyper-shell (BHS) structure of the spurs is reproduced, when a semi-exponential halo model with radially-variable scale height is adopted. A spherical halo model ($\beta$ model) is shown to be not appropriate to explain the observed BHS shape. Asymmetry of the spurs with respect to the rotation axis and to the galactic plane is explained by large-scale density gradient in the halo across the Galaxy. Such gradient may be produced by ram pressure of the IGM during motion of the Galaxy in the Local Group. A halo model having sinusoidal density fluctuations (clouds) can also explain the asymmetry, given appropriate cloud parameters are chosen. Further irregular features such as filaments and multiple curvatures superposed on the spurs are also understood as due to density fluctuations in the halo.

12 pages, 11 figures, to appear in MNRAS

References in corpus (6)

• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• Constraining the Milky Way's Hot Gas Halo with OVII and OVII Emission Lines
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Cited by in corpus (9)

• Simulating the Fermi Bubbles as Forward Shocks Driven by AGN Jets
• Constraining the Distance to the North Polar Spur with Gaia DR2
• Asymmetric eROSITA bubbles as the evidence of a circumgalactic medium wind
• The Central 300 pc of the Galaxy probed by infrared spectra of H3+ and CO: II. Expansion and morphology of the warm diffuse gas
• Probing the Halo Gas Distribution in the Inner Galaxy with Fermi Bubble Observations
• Dark supernova remnant
• One-kpc Expanding Cylinder of HI-Gas around the Galactic Center
• Cosmic-ray electrons and the magnetic field of the North Polar Spur
• Bipolar Molecular Outflow from M17