Hot Gas in the Galactic Thick Disk and Halo Near the Draco Cloud

Abstract

This paper examines the ultraviolet and X-ray photons generated by hot gas in the Galactic thick disk or halo in the Draco region of the northern hemisphere. Our analysis uses the intensities from four ions, C IV, O VI, O VII, and O VIII, sampling temperatures of ~100,000 to ~3,000,000 K. We measured the O VI, O VII and O VIII intensities from FUSE and XMM-Newton data and subtracted off the local contributions in order to deduce the thick disk/halo contributions. These were supplemented with published C IV intensity and O VI column density measurements. Our estimate of the thermal pressure in the O VI-rich thick disk/halo gas, p_{th}/k = 6500^{+2500}_{-2600} K cm^{-3}, suggests that the thick disk/halo is more highly pressurized than would be expected from theoretical analyses. The ratios of C IV to O VI to O VII to O VIII, intensities were compared with those predicted by theoretical models. Gas which was heated to 3,000,000 K then allowed to cool radiatively cannot produce enough C IV or O VI-generated photons per O VII or O VIII-generated photon. Producing enough C IV and O VI emission requires heating additional gas to 100,000 < T < 1,000,000 K. However, shock heating, which provides heating across this temperature range, overproduces O VI relative to the others. Obtaining the observed mix may require a combination of several processes, including some amount of shock heating, heat conduction, and mixing, as well as radiative cooling of very hot gas.

10 pages, 2 figures. Accepted for publication in the Astrophysical Journal

References in corpus (19)

• Turbulent Structure of a Stratified Supernova-Driven Interstellar Medium
• New 3-D gas density maps of NaI and CaII interstellar absorption within 300pc
• X-Ray Absorption from the Milky Way Halo and the Local Group
• The Far Ultraviolet Spectroscopic Explorer Survey of OVI Absorption in the Disk of the Milky Way
• Charge-Transfer induced EUV and Soft X-ray emissions in the Heliosphere
• The Extension of the Transition Temperature Plasma into the Lower Galactic Halo
• OVII and OVIII line emission in the diffuse soft X-ray background: heliospheric and galactic contributions
• A high charge state Coronal Mass Ejection seen through solar wind charge exchange emission as detected by XMM-Newton
• Numerical Study of Turbulent Mixing Layers with Non-Equilibrium Ionization Calculations
• X-ray and UV spectroscopy of Galactic diffuse hot gas along the LMC X--3 sight line
• The SPEAR Instrument and On-Orbit Performance
• An XMM-Newton Survey of the Soft X-ray Background. I. The O VII and O VIII Lines Between l=120 and l=240
• Properties of the Diffuse X-ray Background toward MBM20 with Suzaku
• An Extended FUSE Survey of Diffuse O VI Emission in the Interstellar Medium
• MHD Turbulent Mixing Layers: Equilibrium Cooling Models
• Far-ultraviolet Observations of the North Ecliptic Pole with SPEAR
• X-Ray Searches for Emission from the WHIM in the Galactic Halo and the Intergalactic Medium
• Determining The Galactic Halo's Emission Measure from UV and X-ray Observations
• SPEAR far UV spectral imaging of highly ionized emission from the North Galactic Pole Region

Cited by in corpus (1)

• Characterizing Transition Temperature Gas in the Galactic Corona