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Andrew Fox (ESO-Chile) Jacqueline Bergeron & Patrick Petitjean (IAP-Paris)

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H I H II Si III -Si IV C III -C IV He II -He III N IV -N V O V -O VI 13.6 eV 33.5 eV 47.9 eV 54 eV 77.9 eV 113.9 eV O VI advantages : O VI is most highly ionized line available in rest-frame UV Oxygen is most abundant metal in Universe O VI doublet at 1031, 1037 is intrinsically strong O VI disadvantage : O VI falls in Ly- forest blending/contamination. Only detectable at z 2-3. Energy

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O VI absorbers have power-law column density distribution (Bergeron & Herbert-Fort 2005) Associated or proximate absorbers (at dv

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VLT/UVES Large Program 20 QSOs, high resolution (FWHM 6.6 km s -1 ) and high S/N (~4060) Searched for O VI absorbers within 8000 km s -1 of z QSO. z QSO is determined from several QSO emission lines, allowing for systematic shifts (Tytler & Fan 1992) 35 proximate O VI systems detected: - 26 weak systems - 9 strong systems -200 0 km/s 200

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WEAK log N(O VI )14.5 Weak N V and C IV 1 or 2 components Velocities < z QSO No evidence for partial coverage STRONG o log N(O VI ) 15 o Strong N V and C IV o Multiple components o Velocities clustered around z QSO o Occasional evidence for partial coverage of continuum source. o Truly intrinsic: inflow/outflow near AGN central engine (several mini-BALs)

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Proximity zone extends over ~2000 km s -1, not 5000 km s -1. Intervening systems (Bergeron & Herbert- Fort 2005)

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At 2000 km s -1, see change in N(H I ) and in N(C IV ) but not in N(O VI )

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Significant velocity centroid offsets between O VI and H I are seen in ~50% of the weak O VI absorbers two ions are not co-spatial. (similar fraction of low-z O VI absorbers show offsets; Tripp et al. 2008)

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Median b-values O VI

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Results of Gnat & Sternberg (2007) Frozen-in ionization can lead to O VI being present in gas down to ~10 4 K if the metallicity is close to solar

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YES: Galactic WindsYES: Hot-mode accretion Simulations from Kawata & Rauch (2007)Simulations from Dekel & Birnboim (2007) See also Fangano, Ferrara, & Richter (2007)

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Comparison of high-ion ratios Observations vs theory (Gnat & Sternberg) Cooling gas models can explain data if elemental abundance ratios are non-solar: Need -1.8