Fuse and Stis Observations of Intervening O Vi Absorption Line Systems in the Spectrum of Pg 0953+415

We present Far Ultraviolet Spectroscopic Explorer (FUSE) and Space Telescope Imaging Spectrograph (STIS) observations of the intergalactic medium toward the bright QSO PG 0953+415 (zem = 0.239). The FUSE spectra extend from 905 to 1187 Å have a resolution of 25 km s while the STIS spectra cover 1150 to 1730 have a resolution of 7 km s. Additional STIS observations at 30 km s are obtained in selected wavelength ranges. An O VI system at z = 0.06807 is detected in H I Lyα, Lyβ, Lyγ, O VI λλ1031.93, 1037.62, N V λλ1238.82,1242.80, C IV λλ1548.20,1550.77, and C III λ977.02. The observed column densities can be modeled as a low density intervening gas with a metallicity of 0.4 (+0.6, -0.2) times solar in photoionization equilibrium with the ionizing extragalactic background radiation. The best fit is achieved with an ionization parameter, logU = -1.35, which implies nH ~ 10 -5 cm and a path length of ~ 80 kpc through the absorbing gas. H I Lyα absorption at z = 0.14232 spans a velocity range of 410 km s with the strongest components near 0 and 80 km s in the z = 0.14232 rest frame. In this system O VI λλ1031.93, 1037.62 absorption is strong near 0 km s and not detected at 80 km s. C III λ977.02 absorption is marginally detected at 80 km s but is not detected at 0 km s. The observations place constraints on the properties of the z = 0.14232 system but do not discriminate between collisional 1 Based on observations obtained with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-246555. 2 Based on observations obtained with the WIYN Observatory, which is a joint facility of the University of Wisconsin, Indiana University, Yale University, and the National Optical Astronomy Observatories. 3 Based on observations made with the NASA-CNES-CSA Far-Ultraviolet Spectroscopic Explorer. FUSE is operated for NASA by the Johns Hopkins University under NASA contract NAS-32985. 4 Department of Astronomy, University of Wisconsin-Madison, 475 N. Charter Street, Madison, WI 537061582; [email protected]. 5 Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218; [email protected] 6 Department of Astrophysical Sciences, Princeton University, Princeton, NJ, 08544; [email protected].