Ultra Deep Field Science with the Roman Space Telescope
The wide field of view of the Roman Space Telescope, ~100-200x larger than Hubble, has vast scientific potential not only for the very widest surveys, but also for dramatically expanding Ultra-Deep Field science. Studies of galaxy formation and reionization at the earliest cosmic epochs, to z~9-11 or beyond, require the deepest possible imaging, with depths up to AB~30 achieved in current Hubble Ultra Deep Field science. However, such surveys with Hubble (and JWST in future) remain highly limited in area, typically covering only a few arcminutes, too small to probe large-scale environments or clustering properties, and yielding very small numbers of galaxies at the highest redshifts, all of which are crucial for advancing our understanding of galaxy formation at these very early epochs. Achieving HUDF-quality depth over an area ~100-200x larger becomes readily feasible with the Roman Space Telescope. For example, a notional Ultra Deep Field over a few pointings of the Roman Space Telescope could reach AB~30 in several filters, over ~1 square degree area, with an investment on the order of ~1000 hours. Such a program could expand by ~100x the current handfuls of galaxies at z~9-11, along with thousands of high-z AGN at the faint end of the luminosity function, also over a million faint-end galaxies at more moderate redshifts, tracing their large-scale environments and dramatically increasing the discovery potential at these early epochs of cosmic time.