In my talk I will present results from high-resolution cosmological simulations focusing on the formation of galaxies and black holes during the first few billion years of the Universe. I will discuss how proto-galaxies impact their environments promoting the formation of seed black holes and how in turn these seed black holes affect the growth of their hosting galaxy. Using the high resolution of the simulations I will show predictions on the escape fraction of ionizing photons and make the case that low mass galaxies are the drivers of re-ionization.