Because the same massive stars that reionized the intergalactic medium (IGM) inevitably exploded as supernovae that polluted the Universe with metals, the history of cosmic reionization and enrichment is intimately intertwined. While the overly sensitive Ly α transition completely saturates in a neutral IGM, strong low-ionization metal lines like the $\rm{Mg\, \small {II}}$ λ2796, λ2804 doublet will give rise to a detectable ‘metal-line forest’ if the metals produced during reionization ($Z\sim 10^{-3}\, \mathrm{Z}_{\odot }$) permeate the neutral IGM. We simulate the $\rm{Mg\,\small {II}}$ forest for the first time by combining a large hydrodynamical simulation with a seminumerical reionization topology, assuming a simple enrichment model where the IGM is uniformly suffused with metals. In contrast to the traditional approach of identifying discrete absorbers, we treat the absorption as a continuous random field and measure its two-point correlation function, leveraging techniques from precision cosmology. We show that a realistic mock data set of 10 James Webb Space Telescope spectra can simultaneously determine the Mg abundance, $[{\rm Mg}/{\rm H}]$, with a 1σ precision of 0.02 dex and measure the global neutral fraction $\langle x_{\rm{H\,\small {I}}}\rangle$ to 5 per cent for a Universe with $\langle x_{\rm{H\,\small {I}}}\rangle = 0.74$ and $[{\rm Mg}/ {\rm H}] = -3.7$. Alternatively, if the IGM is pristine, a null detection of the $\rm{Mg\,\small {II}}$ forest would set a stringent upper limit on the IGM metallicity of $[{\rm Mg}/ {\rm H}] \lt -4.4$ at 95 per cent credibility, assuming $\langle x_{\rm{H\,\small {I}}}\rangle \gt 0.5$ from another probe. Concentrations of metals in the circumgalactic environs of galaxies can significantly contaminate the IGM signal, but we demonstrate how these discrete absorbers can be easily identified and masked such that their impact on the correlation function is negligible. The $\rm{Mg\,\small {II}}$ forest thus has tremendous potential to precisely constrain the reionization and enrichment history of the Universe.

中文翻译：

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用 Mg ii 森林探索再电离和早期宇宙富集

由于重新电离星系际介质 (IGM) 的大质量恒星不可避免地爆炸为用金属污染宇宙的超新星，因此宇宙再电离和浓缩的历史密切相关。虽然过度敏感的 Ly α 跃迁在中性 IGM 中完全饱和，但强低电离金属线如 $\rm{Mg\、\small {II}}$ λ2796、λ2804 双峰将产生可检测的“金属线”如果在再电离过程中产生的金属 ($Z\sim 10^{-3}\, \mathrm{Z}_{\odot }$) 渗透到中性 IGM 中。我们首次通过将大型流体动力学模拟与半数值再电离拓扑相结合来模拟 $\rm{Mg\,\small {II}}$ 森林，假设一个简单的富集模型，其中 IGM 均匀地充满金属。与识别离散吸收体的传统方法相比，我们将吸收视为连续随机场，并利用精密宇宙学技术测量其两点相关函数。我们表明，10 个詹姆斯韦伯太空望远镜光谱的真实模拟数据集可以同时确定 Mg 丰度 $[{\rm Mg}/{\rm H}]$，1σ 精度为 0.02 dex，并测量全球中性对于具有 $\langle x_{\rm{H\,\small {I}}}\rangle 的宇宙，分数 $\langle x_{\rm{H\,\small {I}}}\rangle$ 为 5% = 0.74$ 和 $[{\rm Mg}/ {\rm H}] = -3.7$。或者，如果 IGM 是原始的，则 $\rm{Mg\,\small {II}}$ 森林的空检测将对 $[{\rm Mg}/ {\rm 的 IGM 金属丰度设置严格的上限H}] \lt -4.4$，可信度为 95%，假设 $\langle x_{\rm{H\, \small {I}}}\rangle \gt 0.5$ 来自另一个探测器。星系环星系环境中的金属浓度会严重污染 IGM 信号，但我们展示了如何轻松识别和掩盖这些离散吸收体，从而使其对相关函数的影响可以忽略不计。因此，$\rm{Mg\,\small {II}}$ 森林在精确约束宇宙的再电离和富集历史方面具有巨大的潜力。