Tracking Hydrogen Through the Cosmic Ages

最近开始的加拿大氢天文台和无线电瞬态探测器（CHORD）提供了一个前所未有的机会，拼凑出一个不间断的故事，氢是如何通过宇宙时间演变的，包括对附近富氢星系的观测，这些观测可以被详细地解析和研究，以及对遥远宇宙的调查，在那里对来自这些星系的集体无线电发射进行统计检查（“强度映射”）来探测物质的大尺度分布。在实践中，实现这一承诺有两个障碍。首先，不存在一个统一的理论框架来利用这两类观测的互补性。其次，即使有这样一个框架，我们提取科学的能力也只能和我们在CHORD中处理工具系统学的能力一样好。在本提案中，我们应对这两项挑战。在理论方面，我们将建立一个分析框架，能够自洽地模拟单个附近星系和遥远人群的强度映射。利用这一点，我们将回答如何在低红移星系属性的经验约束的关键问题（如如何氢质量跟踪星系中的总质量）可以用来放置高红移强度映射模型的先验。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，包括系统的方式是忠实于什么将在和弦看到。此外，我们面对我们的框架与最终测试的真实的数据从CHORD的早期调试观察。

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.