Mapping the cosmic web with neutral hydrogen during the era of the Square Kilometre Array

宇宙学的一个关键目标是理解宇宙的加速膨胀，这种膨胀被认为是由一种叫做暗能量的力量驱动的。绘制星系在整个宇宙生命周期中的分布可以测量宇宙的膨胀历史，并帮助我们了解暗能量的本质。从历史上看，宇宙学家已经成功地利用星系中恒星的光学发射来绘制宇宙网随时间的变化。在过去的十年中，出现了一种称为强度映射的新方法，它使用气体的无线电发射（特别是高度丰富的中性氢气）来追踪星系的分布。平方公里阵列（SKA）——总部位于曼彻斯特附近的Jodrell Bank——是一个巨大的射电望远镜阵列，将建在澳大利亚和南非的甜点上，具有比任何现有的射电仪器更高的灵敏度和空间分辨率。SKA目前正在建设中，第一批科学验证数据将在2025年左右获得，主要调查将在2028年之后开始。SKA的主要目标之一是观察遥远和微弱星系中的气体，这告诉我们星系是如何随着时间的推移而形成和演化的。SKA观测到的强度图将为我们的宇宙演化提供新的、独立的见解。强度映射是一种独特的探针，因为它可以使用SKA作为单个碟形阵列来观察，也可以在干涉模式下观察，从而在数据中提供更高的空间分辨率。如果我们的目标是全面了解氢如何追踪暗物质，以及气体和星系如何随着宇宙时间演化，这两个数据集都是必不可少的。只有当我们理解了氢与星系的关系，我们才能从强度图中可靠地推断出精确的宇宙学。在这项研究中，我将领导SKA的强度测绘调查的准备工作，以及已经在观测天空的探路者阵列。基于我之前在绿岸望远镜数据强度图上的独特经验，我将建立一个数据分析管道，用于单碟观测的前景和仪器系统学。这种探路者分析将可靠地约束氢的大尺度特性，并利用无线电数据进行先驱膨胀率测量。我将努力检测来自澳大利亚SKA探路者的干涉测量数据中的强度映射信号，同时也是南非MeerKAT团队的一员。这种多项目的方法将有助于我们理解由于仪器和处理系统的分析的复杂性。更高分辨率的强度图将揭示星系中氢含量的信息，以及它在星系团和星系群中的行为。我还将开发新的跨学科方法来探索强度图的潜在科学。这将包括研究星系之间的空白空间，称为空洞，因为它们以一种互补的方式追踪宇宙演化，这种方式较少偏向于天体物理过程。我还将介绍基于压缩感知的新成像技术，这些技术适用于每种科学解释的兴趣尺度，例如空洞分析或星系团。我在SKA探路者数据以及准备未来SKA数据分析管道方面的努力将是至关重要的，以便从强度测绘观测中可靠地推断正确的宇宙学以及天体物理星系演化信息。我将严格限制全球氢的性质和宇宙膨胀率，同时开发新技术，在这些令人兴奋的新观测中寻找未知的物理。

A key goal of cosmology is to understand the accelerated expansion of the Universe, believed to be driven by a force called Dark Energy. Mapping the distribution of galaxies throughout the Universe's lifetime can measure the expansion history and help us understand the nature of Dark Energy. Historically, cosmologists have successfully used the optical emission of stars located in galaxies to map the cosmic web over time. In the past decade, a new method called intensity mapping has emerged which uses the radio emission of gas (specifically the highly abundant Neutral Hydrogen gas) to trace the galaxy distribution. The Square Kilometre Array (SKA) - with headquarters at Jodrell Bank near Manchester - is an enormous radio telescope array to be built in the Australian and South African desserts, capable of higher sensitivities and spatial resolution than any existing radio instrument. The SKA is currently under construction, with first science verification data to come in around 2025, and major surveys to start after 2028. One of the major goals of the SKA is to observe the gas in distant and faint galaxies, which tells us about how galaxies formed and evolved with time. Intensity maps observed by the SKA will give new, independent insights into the evolution of our Universe. Intensity mapping is a unique probe, as it can be observed using the SKA as a single dish array, as well as in interferometric mode which gives much higher spatial resolution in the data. Both datasets are essential if we aim to acquire a complete understanding of how hydrogen traces dark matter and how gas and galaxies evolved with cosmic time. Only when we understand the hydrogen-galaxy relation can we reliably infer precision cosmology from the intensity maps.In this fellowship, I will lead the preparations for intensity mapping surveys with the SKA, as well its pathfinder arrays which are already observing the sky. Building on my exclusive experience with intensity maps from previous work on Green Bank Telescope data, I will establish a data analysis pipeline robust to foregrounds and instrumental systematics for the single dish observations. This pathfinder analysis will reliably constrain the large scale properties of hydrogen and pioneer expansion rate measurements with radio data. I will drive the efforts to detect the intensity mapping signal in interferometric data coming from the Australian SKA pathfinder, while also being part of the South African based MeerKAT team. This multi-project approach will help our understanding of the intricacies of the analysis due to instrumental and processing systematics. The higher resolution intensity maps will reveal information about the hydrogen contents within populations in galaxies and it's behaviour within clusters and groups of galaxies. I will also be developing new, inter-disciplinary approaches to explore the potential science of the intensity maps. This will include studying the empty space between galaxies, called voids, as they trace the cosmic evolution in a complementary way which is less biased through astrophysical processes. I will also introduce new imaging techniques based on compressive sensing, which are adaptable to scales of interest for each scientific interpretation, such as void analysis or galaxy clusters.My efforts on SKA pathfinder data as well as on preparing the future SKA data analysis pipeline will be crucial in order to reliably infer correct cosmology, as well as astrophysical galaxy evolution information from intensity mapping observations. I will put tight constraints on global hydrogen properties and cosmic expansion rates while developing novel techniques to search for unknown physics in these exciting new observations.