THE GLOBAL CONTENT, DISTRIBUTION, AND KINEMATICS OF INTERSTELLAR O vi IN THE LARGE MAGELLANIC CLOUD

We present Far Ultraviolet Spectroscopic Explorer (FUSE) observations of interstellar O vi absorption toward 12 early-type stars in the LargeMagellanic Cloud (LMC). The observations have a velocity resolution of.20 km s 1 (FWHM) and clearly show O vi 1031.926 Å absorption at LMC velocities toward all 12 stars. From these observations we derive column densities of interstellar O vi in this nearby galaxy; the observed columns are in the range logNðO viÞ 1⁄4 13:9–14.6, with a mean of 14.37 and a standard deviation of 38% (þ0:14 0:21 dex). The observations probe several sight lines projected onto known superbubbles in the LMC, but these show relatively little (if any) enhancement in O vi column density compared to sight lines toward relatively quiescent regions of the LMC. The observed LMCO vi absorption is broad, with Gaussian dispersions 30–50 km s 1. This implies temperatures T . ð2 5Þ 106, indicating that much of the broadening is nonthermal because O vi has a very low abundance at such high temperatures. The O vi absorption is typically displaced 30 km s 1 from the corresponding low-ionization absorption associated with the bulk of the LMC gas. The general properties of the LMC O vi absorption are very similar to those of the Milky Way halo. The average column density of O vi and the dispersion of the individual measurements about the mean are identical to those measured for the halo of the Milky Way, even though the metallicity of the LMC is a factor of 2.5 lower than theMilkyWay. The velocity dispersion measured for the LMCmaterial is also consistent with recent measurements of the Galactic halo. The striking similarities in these quantities suggest that much of the LMCO vimay arise in a vertically extended distribution similar to the Galactic halo. We discuss the measurements in the context of a halo composed of radiatively cooling hot gas and/or turbulent mixing layers. If the observed O vi absorption is tracing a radiatively cooling galactic fountain flow, the mass flow rate from one side of the LMC disk is of the order _ M 1M yr 1, with a mass flux per unit area of the disk _ M= 2 10 2 M yr 1 kpc 2. Subject headings: galaxies: ISM — ISM: atoms — Magellanic Clouds — ultraviolet: ISM