Determining The Galactic Halo's Emission Measure from UV and X-ray Observations

Abstract

We analyze a pair of Suzaku shadowing observations in order to determine the X-ray spectrum of the Galaxy's gaseous halo. We simultaneously fit the spectra with models having halo, local, and extragalactic components. The intrinsic intensities of the halo OVII triplet and OVIII Lyman alpha emission lines are 9.98^{+1.10}_{-1.99} LU (line unit; photons cm^-2 s^-1 Sr^-1) and 2.66^{+0.37}_{-0.30} LU, respectively. Meanwhile, FUSE OVI observations for the same directions and SPEAR CIV observations for a nearby direction indicate the existence of hot halo gas at temperatures of ~10^{5.0} K to ~10^{6.0} K. This collection of data implies that the hot gas in the Galactic halo is not isothermal, but its temperature spans a relatively wide range from ~10^{5.0} K to ~10^{7.0} K. We therefore construct a differential emission measure (DEM) model for the halo's hot gas, consisting of two components. In each, dEM/dlog T is assumed to follow a power-law function of the temperature and the gas is assumed to be in collisional ionizational equilibrium. The low-temperature component (LTC) of the broken power-law DEM model covers the temperature range of 10^{4.80}-10^{6.02} K with a slope of 0.30 and the high-temperature component (HTC) covers the temperature range of 10^{6.02}-10^{7.02} K with a slope of -2.21. We find that a simple model in which hot gas accretes onto the Galactic halo and cools radiatively cannot explain both the observed UV and X-ray portions of our broken power-law model. It can, however, explain the intensity in the Suzaku bandpass if the mass infall rate is 1.35*10^{-3} Msun yr^-1 kpc^-2. The UV and X-ray intensities and our broken power-law model can be well explained by hot gas produced by supernova explosions or by supernova remnants supplemented by a smooth source of X-rays.

arXiv comment35 pages, 4 figures, 8 tables. Accepted for publication in ApJ

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Cited by in corpus (16)

• Constraining the Milky Way's Hot Gas Halo with OVII and OVII Emission Lines
• An XMM-Newton Survey of the Soft X-ray Background. III. The Galactic Halo X-ray Emission
• The Interaction of the Fermi Bubbles with the Milky Way's Hot Gas Halo
• Characterizing Transition Temperature Gas in the Galactic Corona
• The Origin of the Hot Gas in the Galactic Halo: Confronting Models with XMM-Newton Observations
• Simulations of High-Velocity Clouds. I. Hydrodynamics and High-Velocity High Ions
• An XMM-Newton Survey of the Soft X-ray Background. II. An All-Sky Catalog of Diffuse O VII and O VIII Emission Intensities
• An XMM-Newton Survey of the Soft X-ray Background. I. The O VII and O VIII Lines Between l=120 and l=240
• HaloSat -- A CubeSat to Study the Hot Galactic Halo
• XMM-Newton and Suzaku X-ray Shadowing Measurements of the Solar Wind Charge Exchange, Local Bubble, and Galactic Halo Emission
• A High Spectral Resolution Study of the Soft X-ray Background with the X-ray Quantum Calorimeter
• Simulations of High-Velocity Clouds. II. Ablation from High-Velocity Clouds as a Source of Low-Velocity High Ions
• Density and metallicity of the Milky-Way circumgalactic gas
• XMM-Newton Measurement of the Galactic Halo X-ray Emission using a Compact Shadowing Cloud
• A Possible Supernova Remnant high above the Galactic Disk
• Hot Gas in the Galactic Thick Disk and Halo Near the Draco Cloud