Galaxy evolution and the reionisation of the Universe

The thesis combines studies of z=3 galaxies as analogs of the first galaxies that were responsible for the process of reionisation of the Universe, with the development of a new technique to measure the total cold gas budget of the Universe and its evolution with time. The combination of these two pieces of work will allow the following objectives to be reached: (1) Determining exactly the cosmic abundance of cold gas in the local Universe, and its partition between the atomic and molecular phases. This will be achieved using data from the xCOLD GASS, ALFALFA and GAMA surveys and the by developing a new Bayesian parameter estimation code. (2) "Turning back the clock" by applying the method to high redshift galaxy samples (e.g. from the PHIBSS survey) to determine the time evolution of the cosmic abundance of gas, and this all the way into the epoch of reionisation. (3) Using the study of the z=3 galaxies to determine how much ionising radiation can leak out of these galaxies. The culmination of this will be in combining the outputs of (2) and (3) to determine if we can find a balance between radiation and abundance of gas in the IGM that explains the reionisation process in a way that is consistent with other constraints.