To probe the distribution and physical characteristics of interstellar gas at temperatures T\ > \approx \ > 3 \times 10 ^ { 5 } K in the disk of the Milky Way , we have used the Far Ultraviolet Spectroscopic Explorer ( FUSE ) to observe absorption lines of O VI \lambda 1032 toward 148 early-type stars situated at distances > \ > 1 kpc .
After subtracting off a mild excess of O VI arising from the Local Bubble , combining our new results with earlier surveys of O VI , and eliminating stars that show conspicuous localized X-ray emission , we find an average O VI mid-plane density n _ { 0 } \ > = \ > 1.3 \times 10 ^ { -8 } { \ > cm } ^ { -3 } .
The density decreases away from the plane of the Galaxy in a way that is consistent with an exponential scale height of 3.2 kpc at negative latitudes or 4.6 kpc at positive latitudes .
Average volume densities of O VI along different sight lines exhibit a dispersion of about 0.26 dex , irrespective of the distances to the target stars .
This indicates that O VI does not arise in randomly situated clouds of a fixed size and density , but instead is distributed in regions that have a very broad range of column densities , with the more strongly absorbing clouds having a lower space density .
Line widths and centroid velocities are much larger than those expected from differential Galactic rotation , but they are nevertheless correlated with distance and N ( O VI ) , which reinforces our picture of a diverse population of hot plasma regions that are ubiquitous over the entire Galactic disk .
The velocity extremes of the O VI profiles show a loose correlation with those of very strong lines of less ionized species , supporting a picture of a turbulent , multiphase medium churned by shock-heated gas from multiple supernova explosions .