The Possible Detection of Cosmological Reionization Sources

We compare the available catalogs of $z\approx6$ galaxies in the HubbleUltra-Deep Field (UDF) and in the Great Observatories Origins Deep Survey(GOODS) with the expected properties of the sources of cosmologicalreionization from our previous theoretical study. Our approach is based on themean surface brightness of the sources required for reionization and depends onrelatively few undetermined parameters. We find that the observed mean surfacebrightness 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 ofredshift. The broad agreement between the new observations and our predictionssuggests that we may have detected the sources responsible for some or even allof the reionization of hydrogen.Comment: ApJL in press. Slightly revised version (mostly wording and some extra references). Original version submitted on 21-March-2004. 10 pages, 1 figur