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

 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 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 Å is intrinsically strong O VI disadvantage : O VI falls in Ly-  forest  blending/contamination. Only detectable at z  2-3. Energy

O VI absorbers have power-law column density distribution (Bergeron & Herbert-Fort 2005) “Associated” or “proximate” absorbers (at dv<5000 km s -1 from QSO) often removed from sample  affected by ionization conditions close to QSO. This talk: Examine this practice (Fox, Bergeron, & Petitjean 2008, MNRAS) VLT/UVES, Keck/HIRES studies Schaye et al Bergeron et al Carswell et al Simcoe et al. 2002,2004,2006 Levshakov et al Reimers et al. 2001, 2006 Bergeron & Herbert-Fort 2005 Lopez et al Gonçalves et al O VI probes IGM ionization and enrichment Is there a proximity effect in O VI ?

 VLT/UVES Large Program  20 QSOs, high resolution (FWHM 6.6 km s -1 ) and high S/N (~40–60)  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 km/s 200

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)

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

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

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)

Median b-values O VI <2000 km s -1 from QSO:  b  =12.3 km s -1 Intervening O VI :  b  =12.7 km s -1  T <1.6x10 5 K Intervening N V :  b  =6.0 km s -1 (Fechner & Richter 2009)  O VI and N V trace different regions O VI Component Line Width Distribution b=  (2kT/m + b 2 non-thermal )

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

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

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<[N/O]< <[C/O]<0.6

 Single-phase photoionization models for IGM O VI absorbers are too simplistic, because 1.O VI -H I velocity offsets imply O 5+ and H 0 occupy different regions 2.O 5+ may be collisionally- rather than photo-ionized 3.Don’t know EGB shape above 100 eV that well  Use caution when combining O VI /H I ratio + CLOUDY  IGM metallicity H 0, O 5+, T~10 4 KH 0, T~10 4 K O 5+, T~10 5 K O 6+, O 7+ T≥10 6 K EGB What you see in H I What you see in O VI

2000 km/s Proximity Warm plasma photoionized as you approach z(QSO), not hot plasma QSO N(H I)~10 15 N(O VI)~ N(H I)~10 14 N(O VI)~

Almost 1 dex uncertainty in J at eV!!! Simcoe et al. (2004)

Madau & Haardt (2009) We don’t really know what’s happening out here!

 In 20 high-quality QSO spectra from UVES, we search for O VI within 8000 kms -1 of z QSO, finding ◦ 9 strong absorbers (truly intrinsic, gas near AGN) ◦ 26 weak absorbers Among weak O VI absorbers:  dN/dz increases by factor of  3 inside 2000 km s -1  dN/dz in range km s -1 matches intervening.  N(H I) and N(C IV ) show a proximity effect (dependence on  v), N(O VI ) does not.  O VI -H I velocity centroid offsets imply at least half the absorbers are multiphase.  Cannot use O VI absorbers to probe high-energy tail of EGB: too many systematic uncertainties. Narrow O VI can form in radiatively-cooling hot gas, in interface regions that result from galactic winds/hot-mode accretion

Partial Coverage of Continuum Source

O VI absorber size is <200 kpc, based on lack of Hubble broadening. Simcoe et al. 2002

 Strong O VI : ◦ Yes, we see strong O VI clustered around z QSO  Weak O VI : ◦ Yes, we see dN/dz increase by a factor of three within 2000 km s -1 (but galaxies are clustered near quasars). ◦ No, the internal properties (b-values, log N) of the O VI absorbers do not depend on  v, unlike H I and C IV No: properties of weak O VI do not require photons at E>100 eV (you can create the O VI with [cooled] hot gas)

 Proximity zone extends over ~2000 km s -1, not 5000 km s convert QSO B-magnitude and z QSO to L 912 (Rollinde et al. 2005) 2.Determine size of “Stromgren Sphere” where QSO radiation density exceeds estimated EGB radiation density at z=2.5 (  ~10 Mpc) 3.Convert size to velocity assuming Hubble Flow and H(z=2.5)=250 km s -1 Mpc -1 (  km s -1 )