16464

We do not empirically know how the first galaxies reionized the early universe. In particular comma how does neutral gas transmit ionizing photons from gas-rich star-forming regions into the intergalactic mediumquestionMark One solution is that small regions of ionized gas preferentially funnel ionizing photons out of galaxies. However comma this anisotropic escape dramatically changes the morphology of cosmic reionization and the subsequent structure of the universe. The James Webb Space Telescope aims to provide the empirical foundation of the epoch of reionization comma but it will not sufficiently resolve the morphology of neutral gas nor the isotropy of the escape of ionizing photons. Here comma we propose 15 orbits of HST mid-cycle observations to obtain 35 pc spatial resolution WFC3 images of the neutral resonant Mg II emission line. The proposed high-ionization emission line galaxy has recently been discovered to have a massive comma but porous comma neutral gas reservoir. Regions of bright resonant Mg II emission will trace the low column density holes through which the newly observed Lyman Alpha must propagate through. These Mg II maps will test where photons are transmitted out of this galaxy to answer how isotropically ionizing photons stream into the intergalactic medium. We will complement the Mg II maps with optical emission line maps to determine whether strong optical lines trace these low column density holes. These observations are crucial for understanding upcoming JWST observations and will illuminate one of the key empirical obstacles towards understanding cosmic reionization.