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B. D. Savage (U. Wisconsin-Madison), K. R. Sembach (STScI), B. P. Wakker, P. Richter, M. Meade (W.Wisconsin-Madison), FUSE Science Team
FUSE spectra of 85 AGNs are analyzed to obtain measures of O VI 1031.93 A absorption along paths through the Milky Way halo. We study the thick disk absorption which covers the velocity range from ~ -100 to 100 km/s. The absorption reveals a widespread but highly irregular distribution of O VI implying substantial amounts of hot (300,000 K) gas in the Milky Way halo. The integrated column density, logN(O VI), ranges from 13.88 to 14.78 with an average of 14.34, while the the O VI column density perpendicular to the Galactic plane, log[N(O VI)sin|b|], ranges from 13.44 to 14.67 with an average of 14.19. Averages of log[N(O VI)sin|b|] over Galactic regions with b > 45 and b < -45 reveal a 0.2 dex excess of O VI to the North compared to the South. The observations are not well described by simple plane parallel models of patchy O VI absorbing structures. The standard deviations for logN(O VI) and logN(O VI)sin|b| are 0.19 and 0.23. The irregularities in the O VI distribution are found to be similar over angular scales extending from several to hundreds of degrees. The O VI profiles range in velocity dispersion, b, from 30 to 99 km/s with an average of 61 km/s and standard deviation of 16 km/s. The O VI average absorption velocities toward high latitude AGNs range from -42 to 82 km/s with an average of 1 km/s and a standard deviation of 22 km/s. The Galactic gas parcels containing O VI are observed to be moving both toward and away from the plane with roughly equal frequency. A combination of models involving the radiative cooling of hot gas in a Galactic fountain flow and the turbulent mixing of warm and hot gases appears to be required to explain the observations. Support from NASA contract NAS5-32985 is appreciated.