宇宙黎明与再电离的理论与观测限制

宇宙黎明和再电离是结构演化的关键阶段，过去一直因观测技术限制而蒙着神秘面纱。如今射电天文技术的发展使之成为全世界激烈竞争的前沿方向。我们在之前的工作中发现了过去理论上的一些重要缺陷，包括宇宙黎明时期21cm整体谱理论和再电离模型上的突破点。在SKA即将进入工程建设阶段之时，本项目将进行必要的模型修正与观测限制研究，并进行巡天策略的设计与优化。研究内容主要包括：（1）宇宙黎明21cm信号的重大修正。精确量化非线性气体密度与温度轮廓对21cm整体谱信号的影响，并进行第一代结构形成的物理参数限制。（2）宇宙再电离的模型检验与观测限制。关注再电离中期，构建适用于整个再电离过程的统一模型，计算可观测信号，研究模型检验方法，并修正再电离历史的观测限制。（3）宇宙黎明与再电离观测的前景模型研究。建立45MHz－200MHz的低频射电天图模型，并研究前景模型的偏差以及不精确扣除对21cm信号提取的影响。

Cosmic dawn and reionization are the key stages in the cosmic history of structure evolution, and have been mysterious for decades due to the observational challenges. The recent advancement in radio astronomy and technologies has made them the research frontier in cosmology with fierce competitions around the world. We have found several important defects in the previous theoretical works, which will result in major breakthroughs, including non-linear effects on the 21 cm global spectrum from cosmic dawn and the drawbacks in the previous reionization modeling. In the era of the SKA entering the construction phase, this project will focus on the necessary corrections of theoretical models and observational constraints, and the design and optimization of the observational strategy. The main research contents include: (1) The major correction of the 21 cm global signal from cosmic dawn. We will precisely quantify the effect of non-linear profiles of gas density as well as the gas temperature on the 21 cm global spectrum signal, and make observational constraints on the physical parameters of the first structure formation during cosmic dawn. (2) The model discrimination and observational constraints on cosmic reionization. We will pay special attention to the mid-epoch of reionization and construct a unified model for the whole reionization process, compute the observational signals, look for the most distinguishable statistics for model discrimination, and make more reliable observational constraints based on the correct model. (3) Construction of the foreground model for radio observation of cosmic dawn and reionization. We plan to develop the low frequency sky model for 45MHz – 200MHz, and study the effects of the possible bias in the foreground model, as well as the inaccurate removal of the foregrounds, on the 21 cm signal extraction.