Probing Cosmic Reionization and Molecular Gas Growth with TIME

Line intensity mapping (LIM) provides a unique and powerful means to probe cosmic structures by measuring the aggregate line emission from all galaxies across redshift. The method is complementary to conventional galaxy redshift surveys that are object-based and demand exquisite point-source sensitivity. The Tomographic Ionized-carbon Mapping Experiment (TIME) will measure the star formation rate (SFR) during cosmic reionization by observing the redshifted [\ion{C}{ii}] 158\,$\mu$m line ($6 \la z \la 9$) in the LIM regime. TIME will simultaneously study the abundance of molecular gas during the era of peak star formation by observing the rotational CO lines emitted by galaxies at $0.5 \la z \la 2$. We present the modeling framework that predicts the constraining power of TIME on a number of observables, including the line luminosity function, and the auto- and cross-correlation power spectra, including synergies with external galaxy tracers. Based on an optimized survey strategy and fiducial model parameters informed by existing observations, we forecast constraints on physical quantities relevant to reionization and galaxy evolution, such as the escape fraction of ionizing photons during reionization, the faint-end slope of the galaxy luminosity function at high redshift, and the cosmic molecular gas density at cosmic noon. We discuss how these constraints can advance our understanding of cosmological galaxy evolution at the two distinct cosmic epochs for TIME, starting in 2021, and how they could be improved in future phases of the experiment.

谱线强度映射（Line Intensity Mapping, LIM）是一种独特且强大的宇宙结构探测手段，通过测量不同红移处所有星系的总谱线辐射来探索宇宙大尺度结构。该方法与传统的基于天体目标、需要极高点源灵敏度的星系红移巡天形成互补。层析电离碳测绘实验（Tomographic Ionized-carbon Mapping Experiment, TIME）将通过在LIM框架下观测红移后的[电离碳II]158微米谱线（6 ≲ z ≲ 9），测量宇宙再电离时期的恒星形成率（Star Formation Rate, SFR）。同时，TIME将通过观测红移0.5 ≲ z ≲ 2的星系辐射的一氧化碳转动谱线，研究恒星形成峰值时期的分子气体丰度。本文构建了可预测TIME对多项可观测物理量约束能力的建模框架，涵盖谱线光度函数、自相关与互相关功率谱，以及与外部星系示踪剂的协同观测潜力。基于优化后的巡天策略以及现有观测所约束的基准模型参数，我们对与再电离和星系演化相关的物理量进行了预测约束，其中包括再电离时期的电离光子逃逸率、高红移星系光度函数的暗端斜率，以及宇宙正午时期的宇宙分子气体密度。我们还讨论了这些约束结果如何推动我们对TIME将于2021年启动的两个独特宇宙纪元的宇宙学星系演化的理解，以及如何在该实验的后续阶段进一步优化这些约束的精度。