The HIX Galaxy Survey - How Hi eXtreme galaxies maintain their Hi reservoir

Our sun is one of one hundred billion stars in the Milky Way and there are billions of galaxies like the Milky Way in the universe. One main objective of modern day astronomy is to understand how these galaxies form and evolve in an attempt to understand the origin of the universe. An important part of galaxy evolution is the formation of stars, for which galaxies need to contain gas. This thesis investigates how galaxies that contain more gas than expected acquire and maintain their gas reservoir.