  The ionizing photons produced by massive stars are key actors in galaxy
evolution. Ionizing photon production and escape is poorly understood. Improved
space-based, spatially-resolved, multiplexed spectroscopic capabilities
covering observed wavelengths of 1000 to 3000 Angstrom, in concert with
spectroscopy from the ELTs and JWST, would lead to definitive answers as to how
ionizing photons are produced and leaked, what populations of galaxies are
responsible for ionizing photon leakage, what determines whether escape is
possible, and how ionizing galaxy populations evolve over cosmic time.
