A view of the entire simulation volume that shows the large-scale structure of the gas distribution in filaments and clumps. The red regions are heated by stellar UV light coming from the galaxies,
highlighted in white. These galaxies are over 1,000 times less massive than the Milky Way and contributed nearly one-third of the UV light during reionization. The field of view of this image is 400,000 light years across when the universe was only 700 million years old.