AI 中文总结
研究利用uGMRT对J352 - 15的观测测量21厘米森林功率谱，通过与模拟光谱比较作贝叶斯推断，虽未统计检测到森林，但联合限制了中性氢分数及温度平均值，不支持特定冷中性IGM模型，显示21厘米森林进入观测信息统计阶段。
AI 中文摘要
由于现有探测手段的限制，再电离时期（EoR）星系际介质（IGM）的中性区域在很大程度上仍未被探索。由于发现了众多高红移射电亮源，21厘米森林，即中性IGM在这些源的光谱中留下的一系列吸收特征，现在为探测\(z\gtrsim5.5\)时主要为中性的IGM的热和电离状态提供了一个有吸引力的探针。我们分析了对J352 - 15（EoR中已知最亮的射电噪类星体，\(z = 5.82\)）的存档升级后的巨型米波射电望远镜（uGMRT）观测数据，以测量21厘米森林的一维功率谱。通过将观测到的功率谱与从涵盖广泛电离和X射线预热场景的宇宙学模拟生成的前向建模合成光谱进行比较，即使在没有统计检测的情况下，我们也进行了贝叶斯推断。我们还展示了默奇森广域阵列的独立测量结果，尽管其较低的灵敏度妨碍了具有竞争力的限制。使用uGMRT，我们在每6.1千赫通道实现了3.62毫焦耳每束的灵敏度。虽然我们没有从统计上检测到21厘米森林，但零检测联合限制了中性氢分数的平均值\(\langle x_{\rm HI}\rangle\)和中性IGM的平均温度\(\langle T_{\rm HI}\rangle\)。在68%的可信水平上，我们的分析不支持\(z\approx5.6\)时冷且基本中性的IGM模型，包括对于\(\langle x_{\rm HI}\rangle = 0.1\)，\(\langle T_{\rm HI}\rangle \lesssim 27\)开尔文的模型。这些限制探测了现有莱曼α和21厘米观测允许的参数空间，表明中性IGM在绝热冷却下限之上有大量的预热。这表明21厘米森林已进入具有观测信息统计的阶段。
英文摘要
Neutral regions of the intergalactic medium (IGM) during the Epoch of Reionization (EoR) remain largely unexplored due to the limitations of existing probes. Owing to discoveries of numerous high-redshift radio-bright sources, the 21-cm forest, a series of absorption features imprinted by the neutral IGM in the spectra of such sources, now offers an attractive probe of the thermal and ionization state of the predominantly neutral IGM at $z\gtrsim5.5$. We analyse archival upgraded Giant Metrewave Radio Telescope (uGMRT) observations of J352-15, the brightest known radio-loud quasar in the EoR ($z=5.82$), to measure the one-dimensional (1D) power spectrum of the 21-cm forest. By comparing the observed power spectrum with forward-modelled synthetic spectra generated from cosmological simulations spanning a wide range of ionization and X-ray pre-heating scenarios, we perform Bayesian inference even in the absence of a statistical detection. We also present an independent Murchison Widefield Array measurement, although its lower sensitivity prevents competitive constraints. Using uGMRT, we achieve a sensitivity of $3.62\,\rm mJy\,beam^{-1}$ per $6.1\,\rm kHz$ channel. While we do not detect the 21-cm forest statistically, the null detection jointly constrains the mean neutral hydrogen fraction, $\langle x_{\rm HI}\rangle$, and the mean temperature of the neutral IGM, $\langle T_{\rm HI}\rangle$. At the $68\%$ credible level, our analysis disfavours cold and substantially neutral IGM models at $z\approx5.6$, including models with $\langle T_{\rm HI}\rangle \lesssim 27\,\rm K$ for $\langle x_{\rm HI}\rangle=0.1$. These limits probe parameter space allowed by existing Ly$α$ and 21-cm observations, indicating substantial pre-heating of the neutral IGM above the adiabatic cooling floor. This demonstrates that the 21-cm forest has entered the regime of observationally informative statistics.
Comments16+3 pages, 12+5 figures, Submitted to Nature Astronomy, Comments welcome
