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Astron. Astrophys. 354, 17-27 (2000)

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5. Conclusion

We observed a sample of 16 high redshift quasars with 2.4[FORMULA]z[FORMULA]3.8 with moderate spectral resolution. We used the emission-line fluxes of NV1240, CIV1549, and HeII1640 to estimate the metallicity of the line emitting gas. We analysed the derived line ratios within the frame work of models presented by Hamann & Ferland (1992, 1993, 1999). The scaled solar abundance model yields inconsistent values for the metallicity provided by NV1240/CIV1549 and NV1240/HeII1640 line ratios. The rapid star formation scenario is successful in indicating the same range of overabundance on base of those line ratios. We estimated an abundance of Z [FORMULA] 8 [FORMULA] given by NV/CIV and NV/HeII. For several quasars of our sample we could also use OVI1034 and the intercombination lines OIII]1663, NV]1750, and CIII]1909 to obtain the relative abundances. These line ratios indicate although with larger scatter within the rapid star formation model metallicities of the order of Z [FORMULA] (3 - 20) [FORMULA].

With an evolution time scale of approximately 1 Gyr the beginning of the first violent star formation could be determinated to a redshift of [FORMULA] [FORMULA] 6 to 10. This result is consistent with cosmological models with [FORMULA]0.3, [FORMULA]0.7, and Ho [FORMULA] 65 km s-1 Mpc-1. In contrast models with significantly smaller Ho and higher [FORMULA] require a much shorter evolutionary time scale otherwise the universe will not be old enough at redshift of z[FORMULA]4.

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© European Southern Observatory (ESO) 2000

Online publication: January 31, 2000