FUSE Observations of Degree-Scale Variations in Galactic Halo O VI

Abstract

We report Far Ultraviolet Spectroscopic Explorer (FUSE) observations of interstellar O VI absorption in the halo of the Milky Way towards 12 early-type stars in the Large Magellanic Cloud (LMC) and 11 in the Small Magellanic Cloud (SMC). The mean column densities of O VI associated with the Galactic halo towards the LMC and SMC are log<N(OVI)> = 14.52(+0.10,-0.14) and 14.13(+0.14,-0.20), respectively, where the uncertainties represent the standard deviations of the individual measurements about the means. Significant variations in the O VI column densities are observed over all of the angular scales probed by our observations: 0.5-5.0 degrees towards the LMC and 0.05-3.3 degrees towards the SMC. The maximum factors by which the O VI varies between sight lines towards the LMC and SMC are ~2.8 and ~4.2, respectively. Though low-, intermediate-, and high-velocity clouds are present along most of the sight lines towards the LMC, the variations in O VI column densities are found in all of these O VI absorbing structures. The column density variations trace the structure of the hot ionized medium in the Galactic halo on scales of <<80 to 800 pc towards the LMC and <<6 to 400 pc towards the SMC (assuming the absorption arises within the first 5 kpc above the Galactic plane).