A New Era in Radio Astronomy: Imaging Neutral Hydrogen Beyond the Local Universe

Gas is the fuel for star formation and a key ingredient in galaxy assembly. We can now obtain radio-wavelength images of the neutral gas in galaxies in our cosmic neighborhood and back across cosmic time to when the Universe was only two thirds its current age. I will discuss how these radio-wavelength data are helping astronomers study gas accretion and removal processes that are constraining cosmological simulations and improving our understanding of how galaxies grow and evolve.