Far‐Ultraviolet Spectroscopic ExplorerObservations 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 toward 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 toward the LMC and SMC are loghNðO viÞi ¼ 14:52 þ0:10 � 0:14 and 14:13 þ0:14 � 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 toward the LMC and 0=05–3=3 toward the SMC. The maximum factors by which the O vi varies between sight lines toward the LMC and SMC are � 2.8 and � 4.2, respectively. Although low-, intermediate-, and high-velocity clouds are present along most of the sight lines toward 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 of580–800 pc toward the LMC and56–400 pc toward the SMC (assuming that the absorption arises within the first 5 kpc above the Galactic plane). Subject headings: ISM: atoms — ISM: structure — ultraviolet: ISM