The Galactic Halo's O VI Resonance Line Intensity

Abstract

We used FUSE to observe ultraviolet emission from diffuse O VI in the hot gas in the Galactic halo. By comparing our result with another, nearby observation blocked by an opaque cloud at a distance of 230 pc, we could subtract off the contribution from the Local Bubble, leading to an apparent halo intensity of I_{OVI} = 4680^{+570}_{-660} photons/cm^2/s/sr. A correction for foreground extinction leads to an intrinsic intensity that could be as much as twice this value. Assuming T ~ 3 x 10^5 K, we conclude that the electron density, n_e, is 0.01-0.02 /cm^3, the thermal pressure, p/k, is 7000-10,000 K/cm^3, and that the hot gas is spread over a length of 50-70 pc, implying a small filling factor for O VI-rich gas. ROSAT observations of emission at 1/4 keV in the same direction indicate that the X-rays are weaker by a factor of 1.1 to 4.7, depending on the foreground extinction. Simulated supernova remnants evolving in low density gas have similar O VI to X-ray ratios when the remnant plasma is approaching collisional ioinizational equilibrium and the physical structures are approaching dynamical ``middle age''. Alternatively, the plasma can be described by a temperature power-law. Assuming that the material is approximately isobaric and the length scales according to T^(beta) d(ln T), we find beta = 1.5+/-0.6 and an upper temperature cutoff of 10^{6.6(+0.3,-0.2)} K. The radiative cooling rate for the hot gas, including that which is too hot to hold O VI, is 6 x 10^{38} erg/s/kpc^2. This rate implies that ~70% of the energy produced in the disk and halo by SN and pre-SN winds is radiated by the hot gas in the halo.

Accepted by the Astrophysical Journal, AASTEX, 39 pages, including 6 figures and 4 tables (manuscript replaced in order to re-typeset Table 3 and correct submission entry)

References in corpus (5)

• Neon Abundances in B-Stars of the Orion Association: Solving the Solar Model Problem?
• Determining solar abundances using helioseismology
• An Extended FUSE Survey of Diffuse O VI Emission in the Interstellar Medium
• The Far Ultraviolet Spectroscopic Explorer Survey of OVI Emission in the Milky Way
• Far-ultraviolet Observations of the North Ecliptic Pole with SPEAR

Cited by in corpus (19)

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• OVII and OVIII line emission in the diffuse soft X-ray background: heliospheric and galactic contributions
• The Trouble with the Local Bubble
• Numerical Study of Turbulent Mixing Layers with Non-Equilibrium Ionization Calculations
• The Rotation of the Hot Gas Around the Milky Way
• The Origin of the Hot Gas in the Galactic Halo: Confronting Models with XMM-Newton Observations
• X-ray and UV spectroscopy of Galactic diffuse hot gas along the LMC X--3 sight line
• Comparing Suzaku and XMM-Newton Observations of the Soft X-ray Background: Evidence for Solar Wind Charge Exchange Emission
• An XMM-Newton Survey of the Soft X-ray Background. I. The O VII and O VIII Lines Between l=120 and l=240
• An XMM-Newton Observation of the Local Bubble Using a Shadowing Filament in the Southern Galactic Hemisphere
• X-ray Spectroscopy of Galactic Hot Gas along the PKS 2155-304 Sight Line
• XMM-Newton and Suzaku X-ray Shadowing Measurements of the Solar Wind Charge Exchange, Local Bubble, and Galactic Halo Emission
• 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
• Simulations of High-Velocity Clouds. II. Ablation from High-Velocity Clouds as a Source of Low-Velocity High Ions
• 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
• A New Analysis of the O VI Emitting Nebula around KPD 0005+5106