Abstract

The reionization of intergalactic hydrogen in the universe's first billion years was likely driven by the first stars and galaxies. However, we will probably never observe these 'first light' sources directly, but their properties can be inferred through accurate measurements of the timeline and morphology of reionization. I will review the observational evidence for reionization and describe how we can use galaxies at our current observational frontiers to measure the reionization process. In particular, Lyman alpha (Lyα) emission from galaxies can be used to probe the intergalactic medium at high redshifts, but requires modelling physics from pc to Gpc scales. I will describe how we can constrain reionization from spectroscopic observations of galaxies, focusing on Lyα emission at z>6, by comparing observations to theoretical models and simulations using statistical inference methods. I will present new measurements which favour a late and relatively rapid reionization, and place these in the context of high redshift galaxy formation. I will discuss the challenges and prospects in understanding reionization and early galaxy evolution with future facilities, such as JWST and upcoming 21cm experiments.