SIMBAD references

A sample of 16 high redshift quasars with 2.4≲z≲3.8 was observed with moderate spectral resolution in the restframe ultraviolet. The emission-line fluxes of NV 1240, CIV 1549, and HeII 1640 were used to estimate the metallicity of the line emitting gas. The line ratios were investigated within the frame work of models presented by Hamann & Ferland (1992ApJ...391L..53H, 1993ApJ...418...11H, 1999ARA&A..37..487H). The scaled solar abundance model yields inconsistent results for the metallicity while the rapid star formation scenario is successful in indicating a common range of overabundance on base of NV 1240/CIV 1549 and NV 1240/HeII 1640 line ratios. We estimated an abundance of Z≃8Z_☉ of the line emitting gas given by NV/CIV and NV/HeII. Assuming an evolution time scale of ∼1Gyr and a cosmological model with Ω_M≃0.3, Ω_Λ≃0.7, and H₀≃65km/s/Mpc the first violent star formation epoch should start at a redshift of z_f≃6 to 10.