Metallicity of the Intergalactic Medium Using Pixel Statistics. IV. Oxygen
Abstract
We have studied the abundance of oxygen in the IGM by analyzing O VI, C IV, Si IV, and H I pixel optical depths derived from a set of high-quality VLT and Keck spectra of 17 QSOs at 2.1lesssim zlesssim 3.6. Comparing ratios τO VI/τC IV(τC IV) 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, which is 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 δ gtrsim 2. Consistent results are obtained by similarly comparing τO VI/τH I(τH I) and τO VI/τSi IV(τSi IV) to simulation values, and also by directly ionization-correcting τO VI/τH I as a function of τH I into [O/H] as a function of density. Subdividing the sample reveals no evidence for evolution, but low- and high-τH I samples are inconsistent, suggesting either density dependence of [O/C] or—more likely—prevalence of collisionally ionized gas at high density.
Based on public data obtained from the ESP archive of observations from the UVES spectrograph at the VLT, Paranal, Chile, and on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The W. M. Keck Observatory was made possible by the generous financial support of the W. M. Keck Foundation.- Publication:
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The Astrophysical Journal
- Pub Date:
- December 2008
- DOI:
- 10.1086/592554
- arXiv:
- arXiv:0712.1239
- Bibcode:
- 2008ApJ...689..851A
- Keywords:
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- cosmology: miscellaneous;
- galaxies: formation;
- intergalactic medium;
- quasars: absorption lines;
- Astrophysics
- E-Print:
- 13 ApJ-style pages, 11 color figures, minor revisions to match version accepted by ApJ