Establishing the era for large-scale radio cosmology

Probing large-scale cosmic structure with wide-sky surveys is a central route to understanding dark energy, dark matter, and the nature of gravity. My proposal will transform a novel technique that uses radio telescopes to map neutral hydrogen gas which traces underlying cosmic structure. By analysing brightness fluctuations in radio intensity maps we can probe gravity, explore the evolution of the Universe and understand primordial inflation. The leading model for explaining our Universe's accelerated expansion and gravitational interactions relies on 95% of its content being unexplained phenomena. Understanding dark energy and dark matter demands either a paradigm shift in physics or an overturning of decades of established results. Secrets regarding the dark sector and tests of general relativity lie within the statistical distribution of the Universe's cosmic web. We currently rely on cataloguing galaxy positions observed around visible wavelengths, to sample the Universe's structure. These galaxy surveys have transformed clustering analysis into a precision science. However, they face major challenges such as i. avoiding systematics unique to optical experiments, ii. measuring density perturbation across "ultra-large" separations, iii. mapping out to distant epochs (beyond redshift ~3). My approach to observational cosmology is fundamentally different and instead maps all radio emission from neutral hydrogen. This provides a far more complete map of the Universe's foundations, leading to more precise clues concerning its origins and evolution. Radio intensity maps are one of the few options available to competitively verify optical survey results (i.). Since it integrates all emission, shot noise is minimal even for vast surveys, hence, it is superior for surveying ultra-large volumes (ii.). Neutral hydrogen stretches back into the very early Universe, thus is a rare tool for probing high redshifts (iii.). Developing radio intensity mapping's potential is thus pivotal for cosmology. For several years I have been a world-leading expert in overcoming the observational challenges facing intensity mapping, such as removing foregrounds that are thousands of times brighter than the cosmological signal we seek. I am already showcasing my successful techniques with pioneering survey data, which demonstrates that the challenges are surmountable. My proposal will evolve radio intensity mapping from an experimental probe into a cosmological workhorse. I am proposing five research objectives, ranging from early ground-breaking results such as first detections of cosmological phenomena at radio wavelengths, up to more advanced projects like probing the conditions of the early Universe and extending intensity mapping into high redshift. The latter objectives begin to fulfil my broad research vision of pushing the frontiers of cosmology. To achieve the goals laid out in this proposal, I will use MeerKAT, precursor to the Square Kilometre Array Observatory (SKAO), which will be the world's largest observatory. I hold leading positions in both collaborations and have delivered ground-breaking results, with more planned using the 4 MeerKAT pilot intensity mapping surveys we already have. Approval has also been secured for a 10,000 square-degree survey with MeerKAT. Commencing within the first half of 2024, MeerKAT will be one of the first to perform a Stage-IV spectroscopic survey of the southern hemisphere sky before being integrated into the SKAO. I will then be uniquely placed to lead an observational campaign with the full SKAO, continuing to address fundamental questions about our Universe. My proposal will pioneer the development of radio intensity mapping into the SKAO era and beyond.