Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...209.8404s&link_type=abstract
2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #84.04; Bulletin of the American Astronomical Society, V
Astronomy and Astrophysics
Astronomy
Scientific paper
We report the OVI resonance line (1032, 1038 Angstroms) intensity of the Milky Way's halo. The intensity was deduced from a pair of FUSE shadowing observations. An observation toward a nearby cloud recorded the Local Bubble's intensity while an observation toward a neighboring, relatively unobscured direction recorded the combined Local Bubble and halo intensity. We attribute the difference in intensity, IOVI = 4680(+570,-660) photons cm-2 s-1 sr-1, to the halo. Given the slight extinction along the second path, the intrinsic intensity may be as much as twice this value. We used the standard method to estimate the electron density, thermal pressure, and pathlength for the OVI-rich gas in the halo, 0.01-0.02 cm-3, 7000-10,000 cm-3 K, and 50-70 pc, respectively. The pathlength is much less than the OVI scale height, suggesting a small filling factor of OVI-rich gas. We compared our FUSE OVI observations with ROSAT soft X-ray observations of the same directions. Depending on the assumed line-of-sight extinction, the halo’s OVI doublet emission is 1.1 to 4.7 times more powerful than its 1/4 keV emission. Simulated supernova remnants evolving in low density gas have similar OVI to X-ray ratios when the remnant plasma is approaching collisional ionizational equilibrium and the physical structures are approaching dynamical “middle age”. Alternatively, the plasma can be described by a temperature power-law. Assuming the material is approximately isobaric and the length (or volume fraction) scales according to Tbetad(lnT), we find beta = 1.5±0.6 and an upper temperature cutoff of 106.6(+0.3,-0.2) K. The radiative cooling rate for all of the gas, including that which is too hot to hold OVI, is 6x1038 erg s-1 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.
Jenkins Edward B.
Sallmen Shauna M.
Shelton Robin L.
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