Finding the stars that reionized the Universe

We study the abundance of the remnants of stars that reionized the Universe in galaxies in the present day Universe using the eagle cosmological hydrodynamical simulation. High mass galaxies contain most of these `reionizers'. The fractional number of galaxies that do not host reionizers increases with decreasing stellar mass, M _*. For the galaxies that host reionizers, the fraction of mass of the galaxy in reionizers increases with decreasing M _*, such that the fraction is low (~10^-4) for high mass galaxies and can be as high as 0.1 in low mass galaxies, M _* <= 10⁷ M_⊙. In Milky-Way like galaxies, the distribution of reionizers is spatially more extended than that of normal stars.