科研之友
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摘要
We use 2167 Sloan Digital Sky Survey quasar spectra to search for low-density oxygen in the intergalactic medium (IGM). Oxygen absorption is detected on a pixel-by-pixel basis by its correlation with Ly alpha forest absorption. We have developed a novel locally calibrated pixel (LCP) search method that uses adjacent regions of the spectrum to calibrate interlopers and spectral artifacts, which would otherwise limit the measurement of OVI absorption. Despite the challenges presented by searching for weak OVI within the Ly alpha forest in spectra of moderate resolution and signal-to-noise, we find a highly significant detection of absorption by oxygen at 2.7 < z < 3.2 (the null hypothesis has a chi(2) = 80 for nine data points). We interpret our results using synthetic spectra generated from a log-normal density field assuming a mixed quasar-galaxy photoionizing background and that it dominates the ionization fraction of detected OVI. The LCP search data can be fit by a constant metallicity model with [O/H] = -2.15(-0.09)(+0.07) but also by models in which low-density regions are unenriched and higher density regions have a higher metallicity. The density-dependent enrichment model by Aguirre et al. is also an acceptable fit. All our successful models have similar mass-weighted oxygen abundance, corresponding to [< O/H >(MW)] = -2.45 +/- 0.06. This result can be used to find the cosmic oxygen density in the Ly alpha forest, Omega(Oxy,IGM) = 1.4(+/- 0.2) x 10(-6) approximate to 3 x 10(-4)Omega(b). This is the tightest constraint on the mass-weighted mean oxygen abundance and the cosmic oxygen density in the Ly alpha forest to date and indicates that it contains approximate to 16% of the total expected metal production by star formation up to z = 3.
- 出版日期2010-6-20
