21 cm Intensity Mapping
After the Universe cooled and atoms first formed with the release of the cosmic microwave background, neutral atomic Hydrogen and dark matter were the primary components constituting matter in the Universe. Fluctuations in the distribution of dark matter, allowed to grow for much of comic history, began to draw in the Hydrogen gas through gravity. Over the course of several billion years, clouds of neutral gas fell towards clumps of dark matter. Eventually this gas collapsed, with gravity overcoming gas pressure to form the first stars and galaxies. Almost all the neutral Hydrogen was subsequently destroyed by the radiation emitted by this first generation of stars and galaxies in a dramatic phase transition called reionization. Clumps of neutral Hydrogen remain however, and it is thought that this gas can provide a rich source of cosmological information through a distinct spectral feature — an emission line with a precise wavelength, 21 cm. If this line can be observed (with radio telescopes) and the neutral Hydrogen mapped across the sky, it would give us an indirect map of large-scale dark matter structures over huge volumes of the Universe. It is hoped that experiments like the Canadian Hydrogen Intensity Mapping Experiment (CHIME, left) will be able to measure the statistical fluctuations in neutral Hydrogen via its 21 cm emission. This is a nascent and exciting new area of observational cosmology.
I am interested in how upcoming 21 cm intensity mapping experiments can be used to constrain cosmological models, with a particular focus on special and general relativistic effects in large-scale structure. I am also interested in how modified gravity models can be constrained with 21 cm maps, and how the statistical signal may be modelled accurately.