Yesterday, we submitted a new paper (arXiv) focusing on the physical properties of the first generations of galaxies in the universe and their role during cosmic reionization.  This effort was led by Hao Xu at UC – San Diego. We analyzed all of the metal-enriched galaxies in the Renaissance Simulations in three different large-scale environments. We found that the galaxy properties are broadly independent on environment and redshift, given that they form during the epoch of reionization. These low-mass galaxies are largely responsible for providing the bulk of ionizing photons to reionization with the fraction of UV photons escaping into the intergalactic medium increasing with decreasing halo mass (~5% at 10^8 solar masses and 40-60% at 10^7 solar masses).  However these small galaxies are vulnerable to feedback suppressing star formation for large periods of time.  Here we quantify this “galaxy-halo occupation fraction” and find that it’s a increasing value (from 10% at 10^7 solar masses to 100% at 3 x 10^8 solar masses) as halos can cool through atomic transitions around 10^8 solar masses.