Ovi, Nv, and Civin the Galactic Halo. II. Velocity‐Resolved Observations with theHubble Space TelescopeandFar Ultraviolet Spectroscopic Explorer

We present a survey of NV and OVI (and where available CIV) in the Galactichalo, using data from the Far Ultraviolet Spectroscopic Explorer (FUSE) and theHubble Space Telescope (HST) along 34 sightlines. These ions are usuallyproduced in nonequilibrium processes such as shocks, evaporative interfaces, orrapidly cooling gas, and thus trace the dynamics of the interstellar medium.Searching for global trends in integrated and velocity-resolved column densityratios, we find large variations in most measures, with some evidence for asystematic trend of higher ionization (lower NV/OVI column density ratio) atlarger positive line-of-sight velocities. The slopes of log[N(NV)/N(OVI)] perunit velocity range from -0.015 to +0.005, with a mean of-0.0032+/-0.0022(r)+/-0.0014(sys) dex/(km/s). We compare this dataset withmodels of velocity-resolved high-ion signatures of several common physicalstructures. The dispersion of the ratios, OVI/NV/CIV, supports the growingbelief that no single model can account for hot halo gas, and in fact somemodels predict much stronger trends than are observed. It is important tounderstand the signatures of different physical structures to interpretspecific lines of sight and future global surveys.Comment: ApJ in press 43 pages, 22 fig