Metal Lines in Cosmological Models of Lyα Absorbers

The metal absorption lines found in association with Lyα absorbers of moderate to high HI column density contain valuable information about the metallicity and ionization conditions within the absorbers and offer a stronger test of models of the intergalactic medium at z ∼ 3 than HI absorption lines alone. We have developed a method to predict the strengths of metal absorption lines within the framework of cosmological models for the Lyα forest. The method consists of evaluating a quantity, the Line Observability Index, for a database of hundreds of candidate metal lines, allowing a comprehensive identification of the lines the model predicts to be detectable associated with a Lyα absorber of a given HI column density and metallicity. Applying this technique to a particular class of models at z ∼ 2 − 4, we predict that the OVI(1032 Å, 1038 Å) doublet is the only practical probe of the metallicity of low column density absorbers (NHI <∼ 10 14.5 cm), that CIV (1548 Å) is the strongest line with rest wavelength λr > 1216 Å regardless of NHI, and that the strongest metal lines should be CIII(977 Å) and SiIII(1206.5 Å), which peak at