Did Galaxies Reionize the Universe?: New Insight from the Hubble Ultra Deep Field 2012

The Hubble Space Telescope (HST) Ultra Deep Field 2012 (UDF12), comprising the deepest near-infrared observations so far acquired by HST, provides our most sensitive probe of the Epoch of Reionization - the period when intergalactic hydrogen was first ionized. Determining which sources provided the necessary ionizing photons for this important transition in cosmic history is a key science goal and one now enabled by the unique sensitivity afforded by the UDF12 program. Using deep WFC3/IR images newly-obtained this year to provide refined and more robust catalogs of the luminosity distribution and intrinsic properties of galaxies at beyond redshift 6, the UDF12 results provide the most detailed information to date on the Epoch of Reionization and the role of early star forming galaxies. We demonstrate the significant advances achieved by the UDF12 in comparison to the earlier UDF datasets and discuss how the UDF12 results serve as our best preparation for future high-redshift science programs with the James Webb Space Telescope later this decade.