宇宙再电离时期莱曼α发射线星系的观测研究

Lyman-alpha emission in high-redshift galaxies offers a unique probe of cosmological reionization, as Lyman-alpha photons are resonantly scattered by neutral hydrogen. We are carrying out a large narrowband imaging survey ‘LAGER’ -- Lyman Alpha Galaxies in the Epoch of Reionization, in search of Lyman-Alpha Emitting galaxies (LAEs) at z~7. The ‘LAGER’ survey is the largest narrowband survey to date for LAEs at z~7, where we are taking narrowband NB964 images in 4 fields with a total area of 12 square degrees. So far, we have completed the first two fields (COSMOS and CDFS). In the COSMOS field, we have identified 27 LAEs, which makes the largest LAE sample at z~7. With this sample, we have found that the Lyman-alpha luminosity function shows a unique pattern in the evolution, with a number density excess at the bright end at z~7. The results imply a cosmic neutral hydrogen fraction of ~40-60% at z~7, supporting the hypothesis of ionized bubbles. We propose to use the full LAGER sample to better constrain the reionization model via studying the luminosity function, the Lyman-alpha visibility, the ionizing volume, and the clustering, and to investigate the formation and evolution of high-redshift galaxies with their photometric and spectroscopic characteristics.

由于中性氢对莱曼α光子的共振散射，极高红移的莱曼α发射线成为研究宇宙再电离的一个独特的探针。我们正在进行一个寻找红移7处的莱曼α发射线星系的观测巡天项目LAGER，来研究再电离时期。该项目是目前最大的利用窄带测光寻找红移7处莱曼α发射线星系的巡天项目。它计划进行4个天区共12平方度的窄带NB964巡天。目前LAGER巡天已完成两个天区的观测，在第一个天区中我们获得了27个莱曼α发射线星系，这是迄今在该红移处最大的样本。利用该样本，我们发现莱曼α发射线星系的光度函数有着独特的演化模式，特别是在亮端出现鼓包。此结果可约束红移7处宇宙中性氢的比例约为40-60%，支持再电离模型中电离泡的假设。我们将继续进行LAGER巡天及其后续的光谱观测，通过研究光度函数、莱曼α发射线分布比例、电离密度和成团性等方法去限制宇宙再电离模型，并通过分析该红移处星系样本的测光和光谱特征，研究极高红移星系的形成和演化。

本项目依托我们正在进行的LAGER巡天开展对宇宙再电离时期星系的系统搜寻和研究工作，以该样本星系探索宇宙再电离为主要科学目标。我们重点研究了通过光度函数演化来限制宇宙再电离时期红移6.9处的中性氢比例。本项目取得的研究成果包括：1）构建红移6.9处最大的莱曼发射线星系样本；2）利用红移6.9处莱曼发射线星系的莱曼线光度函数，通过比较它与低红移处星系光度函数的演化，探索发现红移6.9处中性氢比例比之前认识的要低；3）发现最高红移处（即最遥远）的具有光谱证认的原初星系团（红移6.9）；4）统计研究LAGER选低红移发射线星系的性质。