We examine rest-frame ultraviolet spectra of 70 high-redshift quasars (z ≥ 3.5) to study the chemical enrichment history of the gas closely related to the quasars and thereby estimate the epoch of first star formation. The fluxes of several ultraviolet emission lines were investigated within the framework of the most recent photoionization models to estimate the metallicity of the gas associated with the high-redshift quasars. Standard photoionization parameters and the assumption of secondary nitrogen enrichment indicate an average abundance of Z/Solar luminosity appro= 4-5 in the line-emitting gas. Assuming a timescale of τ_(evol) approx= 0.5-0.8 Gyr for the chemical enrichment of the gas, the first major star formation for quasars with z approx= 4 should have started at a redshift of z_f approx= 6-8, corresponding to an age of the universe of several times 10~8 yr (H_0 = 65 km s~(-1) Mpc~(-1), Ω_M = 0.3, Ω_Λ = 0.7). We note that this also appears to be the era of reionization of the universe. Finally, there is some evidence for a positive luminosity-metallicity relation in this high-redshift quasar sample.
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机译：我们检查了70个高红移类星体（z≥3.5）的静止帧紫外光谱，以研究与类星体密切相关的气体的化学富集历史，从而估计了第一颗恒星形成的时期。在最新的光电离模型的框架内研究了几种紫外线发射线的通量，以估计与高红移类星体相关的气体的金属性。标准光电离参数和二次氮富集的假设表明，在发射线的气体中Z /太阳光度的平均丰度约为4-5。假设气体化学富集的时间尺度τ_（evol）大约为0.5-0.8 Gyr，则z近似为4的类星体的第一个主要恒星形成应该以z_f近似为6-8的红移开始。宇宙年龄为10〜8年（H_0 = 65 km s〜（-1）Mpc〜（-1），Ω_M= 0.3，Ω_Λ= 0.7）。我们注意到，这似乎也是宇宙电离的时代。最后，有一些证据表明这种高红移类星体样品具有正光度-金属度关系。
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