Tracking Hydrogen Through the Cosmic Ages

最近开始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来拼凑一个关于氢如何在宇宙时间中演化的不间断故事，包括对附近富氢星系的近距离观测，这些星系可以得到详细的解析和研究，以及对遥远宇宙的调查，在那里对这些星系的集体射电辐射进行统计检查(“强度图”)，以探索物质的大尺度分布-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察的互补性。其次，即使有了这样的框架，我们提取科学的能力也只能与我们处理和弦中的乐器系统学的能力一样好。在这项提案中，我们解决了这两个挑战。在理论方面，我们将建立一个分析框架，能够自始至终地模拟附近的单个星系和绘制遥远星系群的强度图。利用这一点，我们将回答一些关键问题，即如何使用对低红移星系属性的经验约束(例如，氢质量如何跟踪星系中的总质量)来为高红移强度映射模型设置先验条件。有了这样的校准模型，我们将使用和弦观测的端到端模拟来批判性地检查单个星系观测和强度映射可以相互补充的方式。我们将制作一系列明确的预测，其中包括系统学，其方式与Chord中将看到的情况相一致。此外，我们对我们的框架进行了最终测试，测试的实际数据来自Chord的早期试运行观察。

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.