在暗区中堆叠HI：迈向探测再电离纪元莱曼-$\alpha$暗隙中的21厘米信号
Stacking HI in the dark: Towards detecting the reionization-epoch 21 cm signal in Lyman-$α$ dark gaps
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中文总结 AI 辅助
提出利用类星体吸收光谱暗隙引导的实空间堆叠技术，探测再电离纪元21厘米信号，模拟显示约100个暗隙可实现信噪比超10的稳健探测。
中文摘要 AI 辅助
对再电离纪元期间中性氢的红移21厘米信号的探测仍然是当代宇宙学的核心挑战之一。尽管即将到来的射电干涉仪预计能以百分之几的精度测量21厘米涨落，但独立的确认对于确保免受仪器系统效应和前景污染的稳健性至关重要。在这项工作中，我们提出了一种新颖的实空间堆叠技术来探测21厘米信号，该技术以再电离晚期（$z \sim 5.0$-$6.1$）类星体吸收光谱中暗隙的存在为指导。利用半数值再电离模型，我们表明，在长暗隙（长度$L > 32~h^{-1}\mathrm{cMpc}$，阈值通量$F_{\mathrm{th}} < 0.005$）上堆叠21厘米图像应揭示一个强发射信号，其峰值平均减除21厘米亮温度$\delta \tilde{T}_b \sim 2-3~ mK$，对应于$z = 5.9$处体积加权平均中性分数$x_{\mathrm{HI}} \sim 0.1$。我们进一步将分析扩展到真实的再电离光锥，结合热噪声和前景规避效应，为两种不同的再电离历史生成。在乐观的前景规避场景（楔形视场$\theta < 20^\circ$）中，约100个暗隙的样本足以对两种再电离模型实现超过10的组合均方根信噪比，而更保守的楔形规避可能需要更多暗隙以实现可靠探测。鉴于已知$z > 6$的类星体数量众多，对这种堆叠信号的探测可能已经处于现有光学（即VLT、Keck）和21厘米观测站（即HERA、SKA）的能力范围内。这种协同方法为直接且统计稳健地探测宇宙学21厘米信号提供了一条有前景的途径。
英文摘要
The detection of the redshifted 21 cm signal from neutral hydrogen during the epoch of reionization remains one of the central challenges in contemporary cosmology. Although upcoming radio interferometers are expected to measure 21 cm fluctuations at a few percent precision, an independent confirmation is essential to ensure robustness against instrumental systematics and foreground contamination. In this work, we propose a novel real-space stacking technique to detect the 21 cm signal, guided by the presence of dark gaps in quasar absorption spectra during the late stages of reionization ($z \sim 5.0$-$6.1$). Using a semi-numerical reionization model, we show that stacking 21 cm images on long dark gaps (length, $L > 32~h^{-1}\mathrm{cMpc}$ and threshold flux, $F_{\mathrm{th}} < 0.005$) should reveal a strong emission signal with a peak mean-subtracted 21 cm brightness temperature of $δ\tilde{T}_b \sim 2-3~ mK$ for a volume-weighted average neutral fraction of $x_{\mathrm{HI}} \sim 0.1$ at $z = 5.9$. We further extend our analysis to realistic reionization lightcones, incorporating thermal noise and foreground avoidance effects, generated for two different reionization histories. In an optimistic foreground avoidance scenario (wedge field of view $θ< 20^\circ$), a sample of roughly 100 dark gaps is sufficient to achieve a combined root-sum-square signal-to-noise ratio exceeding 10 for both reionization models, while a more conservative wedge avoidance may require more dark gaps for a solid detection. Given the large number of quasars known at $z > 6$, a detection of this stacked signal may thus already be within reach of existing optical (i.e., VLT, Keck) and 21 cm observatories (i.e., HERA, SKA). This synergistic approach offers a promising pathway towards a direct and statistically robust detection of the cosmological 21 cm signal.
发表机构
- Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）
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