The Distribution of Metallicity in the Intergalactic Medium at z ~ 2.5: O VI and C IV Absorption in the Spectra of Seven QSOs
The Distribution of Metallicity in the Intergalactic Medium at z ~ 2.5: O VI and C IV Absorption in the Spectra of Seven QSOs
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z ~ 2.5 处星系际介质中金属丰度的分布：七个 QSO 光谱中的 O VI 和 C IV 吸收
DOI：
10.1086/382777
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
M. Rauch
中科院分区：
文献类型：
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作者：
R. Simcoe;W. Sargent;M. Rauch
我们提出了高红移星际介质（IGM）金属丰度分布函数的直接测量。我们使用生存统计数据确定该函数的形状，其中包含与高分辨率类星体光谱中的 H I 线相关的 O VI 和 C IV 吸收的检测和未检测。 O VI 样本（取自 zabs ~ 2.5 处的七个 QSO）包含 N ≥ 1013.6 的线，涵盖 z ~ 2.5 处所有重子的 ~50%。我们的调查占了该时期宇宙中约 98.8% 的 C IV 质量和约 90% 的 O VI 质量。我们发现星系间丰度中位数为 [O,C/H] = -2.82；差异丰度分布近似对数正态分布，平均值 ≈ -2.85，σ = 0.75 dex。我们讨论这些结果对电离紫外线辐射场的假设形式的敏感性。 Lyα 森林中约 60%-70% 的品系富集到可观察到的 [O,C/H] ≳ -3.5 水平，而其余约 30% 的品系丰度甚至更低。因此，我们没有检测到通用金属丰度下限，正如某些第三族富集情景所建议的那样。事实上，我们认为大部分星系间金属的形成晚于被认为引发再电离的第一批恒星。我们没有观察到金属丰度向较低密度 IGM 方向降低的强烈趋势，至少在数值模拟中被表征为细丝的区域内。然而，[O/H] 增强可能会以较高的密度出现。我们估计，在这些红移处，大约一半的重子已富集到 [O,C/H] ≳ -3.5。使用简单的 IGM 金属丰度演化的“封闭盒”模型，我们估计了 z ~ 2.5 之前形成的星系的化学产率，发现典型星系在大爆炸后的前 3 Gyr 中将其质量的 0.1%-0.4% 作为重元素回收回 IGM。
We present a direct measurement of the metallicity distribution function for the high-redshift intergalactic medium (IGM). We determine the shape of this function using survival statistics, which incorporate both detections and nondetections of O VI and C IV absorption, associated with H I lines in high-resolution quasar spectra. The O VI sample (taken from seven QSOs at zabs ~ 2.5) contains lines with N ≥ 1013.6, encompassing ~50% of all baryons at z ~ 2.5. Our survey accounts for ≈98.8% of the C IV mass and ≈90% of the O VI mass in the universe at this epoch. We find a median intergalactic abundance of [O,C/H] = -2.82; the differential abundance distribution is approximately lognormal with mean ≈ -2.85 and σ = 0.75 dex. We discuss the sensitivity of these results to the assumed form of the ionizing UV radiation field. Some ~60%-70% of lines in the Lyα forest are enriched to observable levels of [O,C/H] ≳ -3.5, while the remaining ~30% of the lines have even lower abundances. Thus we have not detected a universal metallicity floor, as has been suggested for some Population III enrichment scenarios. In fact, we argue that the bulk of the intergalactic metals formed later than the first stars that are thought to have triggered reionization. We do not observe a strong trend of decreasing metallicity toward the lower density IGM, at least within regions that would be characterized as filaments in numerical simulations. However, an [O/H] enhancement may be present at somewhat high densities. We estimate that roughly half of all baryons at these redshifts have been enriched to [O,C/H] ≳ -3.5. Using a simple "closed box" model for the metallicity evolution of the IGM, we estimate the chemical yield of galaxies formed prior to z ~ 2.5, finding that the typical galaxy recycled 0.1%-0.4% of its mass back into the IGM as heavy elements in the first 3 Gyr after the big bang.