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T.M. Tripp, D.V. Bowen, E.B. Jenkins (Princeton Obs.), B.D. Savage (U. Wisconsin-Madison)
We present high resolution FUV echelle spectroscopy of several low z intervening O VI absorbers (z < 0.3) in the spectra of H1821+643 and PG0953+415. The data were obtained with the Space Telescope Imaging Spectrograph at a resolution of ~45,000 (7 km/s FWHM). We also present selected new measurements of galaxy redshifts in the 10' field centered on H1821+643. The observations provide several clues about the nature of these absorbers: (1) In the case of the strong O VI system at z = 0.2250 in the spectrum of H1821+643, we detect multicomponent Si II and Si III absorption as well as O VI and several Lyman series lines of H I. Multiple components are evident in the O VI profiles, but the components have different velocities than the Si III and Si II lines. Furthermore, the Si II and Si III lines are quite narrow, and the O VI lines are broader and spread over a larger velocity range. This evidence strongly indicates that this is a multiphase absorber. (2) We also detect `high velocity' O VI in the z = 0.2250 system. High velocity H I is also seen in the Ly\alpha profile, but substantially offset in velocity from the O VI. This high velocity O VI may be analogous to the highly ionized high velocity clouds seen near the Milky Way. (3) We also present systems at other redshifts including very weak O VI absorption lines accompanied by weak and narrow H I absorption. (4) In all cases, several galaxies are close to the sight lines at the redshift of the O VI systems. We examine whether the O VI absorption can be attributed to the ISM of a single galaxy or the intragroup medium.