Andrew Fox (ESO-Chile) Jacqueline Bergeron & Patrick
Petitjean (IAP-Paris)
Slide 2
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
Slide 3
O VI absorbers have power-law column density distribution
(Bergeron & Herbert-Fort 2005) Associated or proximate
absorbers (at dv
Slide 4
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
Slide 5
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)
Slide 6
Proximity zone extends over ~2000 km s -1, not 5000 km s -1.
Intervening systems (Bergeron & Herbert- Fort 2005)
Slide 7
At 2000 km s -1, see change in N(H I ) and in N(C IV ) but not
in N(O VI )
Slide 8
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)
Slide 9
Median b-values O VI
Slide 10
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
Slide 11
YES: Galactic WindsYES: Hot-mode accretion Simulations from
Kawata & Rauch (2007)Simulations from Dekel & Birnboim
(2007) See also Fangano, Ferrara, & Richter (2007)
Slide 12
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