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Title
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Metallicity of the intergalactic medium using pixel statistics : 4 : oxygen
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Author
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Abstract
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| 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 ] approx 1.4, which is highly inconsistent with the [ Si/O ] approx 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] ormore likelyprevalence of collisionally ionized gas at high density. |
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Language
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English
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Source (journal)
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The astrophysical journal. - Chicago, Ill., 1895, currens
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Publication
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Chicago, Ill.
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2008
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ISSN
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0004-637X
[print]
1538-4357
[online]
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DOI
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10.1086/592554
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Volume/pages
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689
:2
(2008)
, p. 851-864
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ISI
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000261189600015
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Full text (Publisher's DOI)
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