The Origin of the Hot Gas in the Galactic Halo: Testing Galactic Fountain Models' X-ray Emission

Abstract

We test the X-ray emission predictions of galactic fountain models against XMM-Newton measurements of the emission from the Milky Way's hot halo. These measurements are from 110 sight lines, spanning the full range of Galactic longitudes. We find that a magnetohydrodynamical simulation of a supernova-driven interstellar medium, which features a flow of hot gas from the disk to the halo, reproduces the temperature but significantly underpredicts the 0.5-2.0 keV surface brightness of the halo (by two orders of magnitude, if we compare the median predicted and observed values). This is true for versions of the model with and without an interstellar magnetic field. We consider different reasons for the discrepancy between the model predictions and the observations. We find taking into account overionization in cooled halo plasma, which could in principle boost the predicted X-ray emission, is unlikely in practice to bring the predictions in line with the observations. We also find that including thermal conduction, which would tend to increase the surface brightnesses of interfaces between hot and cold gas, would not overcome the surface brightness shortfall. However, charge exchange emission from such interfaces, not included in the current model, may be significant. The faintness of the model may also be due to the lack of cosmic ray driving, meaning that the model may underestimate the amount of material transported from the disk to halo. In addition, an extended hot halo of accreted material may be important, by supplying hot electrons that could boost the emission of the material driven out from the disk. Additional model predictions are needed to test the relative importance of these processes in explaining the observed halo emission.

11 pages, 3 figures. Accepted for publication in the Astrophysical Journal

References in corpus (8)

• Turbulent Structure of a Stratified Supernova-Driven Interstellar Medium
• Dependence of Interstellar Turbulent Pressure on Supernova Rate
• Vertical structure of a supernova-driven turbulent magnetized ISM
• X-ray coronae in simulations of disc galaxy formation
• X-Ray Absorption from the Milky Way Halo and the Local Group
• OVII and OVIII line emission in the diffuse soft X-ray background: heliospheric and galactic contributions
• X-ray and UV spectroscopy of Galactic diffuse hot gas along the LMC X--3 sight line
• XMM-Newton Measurement of the Galactic Halo X-ray Emission using a Compact Shadowing Cloud

Cited by in corpus (8)

• 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
• The distribution of mean and fluctuating magnetic fields in the multi-phase ISM
• The SATIN project I: Turbulent multi-phase ISM in Milky Way simulations with SNe feedback from stellar clusters
• On the Kinematics of Cold, Metal-enriched Galactic Fountain Flows in Nearby Star-forming Galaxies
• Topological signatures of interstellar magnetic fields - I. Betti numbers and persistence diagrams
• Introducing the Condor Array Telescope: IV. A possible nova super-remnant surrounding the putative recurrent nova KT Eridani
• An Empirical Determination of the Dependence of the Circumgalactic Mass Cooling Rate and Feedback Mass Loading Factor on Galactic Stellar Mass
• Tracing the Origins of Hot Halo Gas in Milky Way-Type Galaxies with SMUGGLE