The reionization of the intergalactic medium (IGM) at z>6 is likely driven by the first stars and galaxies, but it is still unclear whether galaxies can produce the required ionizing photons and we do not understand the interactions between these early galaxies and their surrounding media. I will describe two key ways in which observations of galaxies can answer these questions and constrain reionization.
One tool is the UV luminosity function, which traces the evolution of star forming galaxies and their ionizing photons. I will describe a simple, but powerful, model for LF evolution and its implications for reionization. Secondly, Lyman alpha emission from galaxies is a potential probe of the ionization state of the IGM. I will introduce a new forward-modeling approach which simultaneously incorporates realistic simulated IGM reionization topologies and interstellar medium conditions to infer the IGM ionized fraction from Lya observations. I will describe ongoing efforts to build large samples of Lya emitting galaxies with the HST grism survey GLASS, and show how observations with JWST will reveal more about early galaxies and the nature of reionization.
