Possible Detection of Cosmological Reionization Sources

We compare the available catalogs of $z\approx6$ galaxies in the Hubble Ultra-Deep Field (UDF) and in the Great Observatories Origins Deep Survey (GOODS) with the expected properties of the sources of cosmological reionization from our previous theoretical study. Our approach is based on the mean surface brightness of the sources required for reionization and depends on relatively few undetermined parameters. We find that the observed mean surface brightness of galaxies at $z \approx 6$ is sufficient for reionization, provided that the sources are composed of hot metal-free or metal-poor stars, regardless of whether reionization occurs over a short or long interval of redshift. The broad agreement between the new observations and our predictions suggests that we may have detected the sources responsible for some or even all of the reionization of hydrogen.