Exploring neutral hydrogen and galaxy evolution with the SKA

One of the key science drivers for the development of the SKA is to observe the neutral hydrogen, H I , in galaxies as a means to probe galaxy evolution across a range of environments over cosmic time. Over the past decade, much progress has been made in theoretical simulations and observations of H I in galaxies. However, recent H I surveys on both single dish radio telescopes and interferometers, while providing detailed information on global H I properties, the dark matter distribution in galaxies, as well as insight into the relationship between star formation and the interstellar medium, have been limited to the local universe. Ongoing and upcoming H I surveys on SKA pathfinder instruments will extend these measurements beyond the local universe to intermediate redshifts. We present here an overview of the H I science which will be possible with the the SKA and which will build upon the expected increase in knowledge of H I in and around galaxies obtained with the SKA pathfinder surveys. With the SKA1 the greatest improvement is the capability to image galaxies at reasonable linear resolution and good column density sensitivity to much higer redshifts (0:2 < z < 1:7). So one will not only be able to increase the number of detections to study the evolution of the H I mass function, but also have the sensitivity and resolution to study inflows and outflows to and from galaxies and the kinematics of the gas within and around galaxies as a function of environment and cosmic time out to previously unexplored depths. The increased sensitivity of SKA2 will allow us to image Milky Way-size galaxies out to redshifts of z = 1 and will provide the data required for a comprehensive picture of the H I content of galaxies back to z ∼ 2 when the cosmic star formation rate density was at its peak.