Metallicity of the intergalactic medium using pixel statistics: IV. Oxygen

Abstract

We have studied the abundance of oxygen in the IGM by analyzing OVI, CIV, SiIV, and HI pixel optical depths derived from a set of high-quality VLT and Keck spectra of 17 QSOs at 2.1 < z < 3.6. Comparing OVI and CIV optical depth ratios to those in realistic, synthetic spectra drawn from a hydrodynamical simulation and comparing to existing constraints on [Si/C] places strong constraints on the ultraviolet background (UVB) model using weak priors on allowed values of [Si/O]: for example, a quasar-only background yields [Si/O] ~ 1.4, highly inconsistent with the [Si/O] ~ 0 expected from nucleosynthetic yields and with observations of metal-poor stars. Assuming a fiducial quasar+galaxy UVB consistent with these constraints yields a primary result that [O/C] = 0.66 +/- 0.06 +/- 0.2; this result pertains to gas with overdensity >~ 0.2. Consistent results are obtained by similarly comparing OVI to HI or OVI to SiIV optical depth ratios to simulation values, and also by directly ionization-correcting OVI optical depths as function of HI optical depths into [O/H] as a function of density. Subdividing the sample reveals no evidence for evolution, but low- and high-density samples are inconsistent, suggesting either density-dependence of [O/C] or -- more likely -- prevalence of collisionally-ionized gas at high density.

13 ApJ-style pages, 11 color figures, minor revisions to match version accepted by ApJ

References in corpus (5)

• Cosmological Simulations of Intergalactic Medium Enrichment from Galactic Outflows
• A large population of metal-rich, compact, intergalactic C IV absorbers - Evidence for poor small-scale metal mixing
• The missing metals problem. III How many metals are expelled from galaxies?
• Intergalactic CIV absorption at redshifts 5.4 to 6
• High Redshift Intergalactic C IV Abundance Measurements from the Near-Infrared Spectra of Two z~6 QSOs

Cited by in corpus (5)

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• Chemical enrichment in cosmological, smoothed particle hydrodynamics simulations
• Cosmological Simulations of Intergalactic Medium Enrichment from Galactic Outflows
• The nature of NV absorbers at high redshift
• Evidence for overdensity around z_em > 4 quasars from the proximity effect