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

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.