The Panoramic Perspective on Gas and Galaxy Evolution

Understanding the physical processes that govern the formation and evolution of galaxies and their constituent stars in different cosmic environments, is at the forefront of contemporary astrophysical research. The detailed distribution and motions of atomic hydrogen (HI) in and around galaxies, observable at radio wavelengths, are uniquely sensitive tracers of these physical processes. To study these processes, I will, for the first time, chart the HI gas in a hundred thousand galaxies covering all environments over the past 3 billion years of cosmic evolution. These data will increase the existing body of observational evidence a thousand-fold. I will perform this survey using APERTIF, an innovative, Dutch, panoramic radio camera developed for the Westerbork telescope. APERTIF is fully funded by NWO and will become operational next year. I will lead my group in early-science exploitation of APERTIF and carry out the Medium-Deep HI Survey. In particular, I will 1) based on an early-science program, characterise the HI gas in galaxies to facilitate a meaningful physical interpretation of their properties. This will focus on the complete Ursa Major group of galaxies, allowing the determination of the HI mass function and the analysis of local environments in this region; 2) build a database structure to accommodate ancillary data required for a broad astrophysical interpretation of APERTIF data, enabling to study the star formation in Ursa Major galaxies in the context of their detailed HI distributions and kinematics 3) compare observational results from APERTIF with detailed computer simulations of galaxy formation and explore which observed properties of the HI gas are most useful to guide these simulations, and 4) use data from the early stages of the Medium-Deep Survey to study the environmental dependence of the physical mechanisms responsible for the accretion and depletion of HI in galaxies at distances up to 3 billion light years.