Tracking Hydrogen Through the Cosmic Ages

最近启动的加拿大氢天文台和无线电瞬变探测器（CHORD）提供了一个前所未有的机会，可以不间断地拼凑出氢在宇宙时间中如何演化的故事，包括附近富氢星系的观测，可以解决和详细研究，以及对遥远宇宙的调查，这些星系的集体射电发射被统计地检查（“强度映射”），以探测物质的大规模分布-原则上。在实践中，实现这一承诺有两个障碍。首先，没有一个统一的理论框架来利用这两种观测的互补性。其次，即使有了这样一个框架，我们提取科学的能力也只能和我们在CHORD中处理仪器系统的能力一样好。在本提案中，我们应对这两个挑战。在理论方面，我们将建立一个分析框架，能够自我一致地模拟附近的单个星系和遥远种群的强度映射。利用这一点，我们将回答关键问题，即如何在低红移时对星系特性的经验约束（例如氢质量如何跟踪星系中的总质量）可以用于在高红移强度映射模型上放置先验。有了这样的校准模型，我们将使用CHORD观测的端到端模拟来严格检查单个星系观测和强度映射可以相互补充的方式。我们将产生一系列明确的预测，其中包括以一种忠实于将在CHORD中看到的方式进行的系统分析。此外，我们还对从CHORD早期调试观察中获得的真实数据进行了最终测试。

The recently commenced Canadian Hydrogen Observatory and Radio-transient Detector (CHORD) provides an unprecedented opportunity to piece together an uninterrupted story of how hydrogen evolved through cosmic time, encompassing nearby observations of nearby hydrogen-rich galaxies that can be resolved and studied in detail as well as surveys of the distant universe where the collective radio emission from these galaxies is examined statistically ("intensity mapping") to probe the large-scale distribution of matter---in principle. In practice, there are two hurdles to realizing this promise. First, there does not exist a unified theoretical framework for exploiting the complementarity of the two types of observations. Second, even with such a framework, our ability to extract science will only be as good as our ability to deal with instrumental systematics in CHORD. In this proposal we address both challenges. On the theoretical front we will establish an analysis framework capable of self-consistently modelling both individual nearby galaxies and the intensity mapping of distant populations. Using this, we will then answer key questions of how empirical constraints on galaxy properties at low redshifts (such as how hydrogen mass traces total mass in a galaxy) can be used to place priors on high-redshift intensity mapping models. With such calibrated models we will use end-to-end simulations of CHORD observations to critically examine the way in which individual galaxy observations and intensity mapping can complement each other. We will produce a series of definitive forecasts that include systematics in a way that is faithful to what will be seen in CHORD. Additionally, we confront our framework with the ultimate test of real data obtained from CHORD's early commissioning observations.