Direct Evidence for an Early Reionization of the Universe?

We examine the possible reionization of the intergalactic medium by the source UDF 033238.7-274839.8 (hereafter HUDF-JD2), which was discovered in deep HST/VLT/Spitzer images obtained as part of the Great Observatories Origins Deep Survey and Hubble Ultra Deep Field projects. Mobasher et al. have identified HUDF-JD2 as a massive (~6 × 1011 M☉) post-starburst galaxy at redshift z ≳ 6.5. We find that HUDF-JD2 may be capable of reionizing its surrounding region of the universe, starting the process at a redshift as high as z ≈ 15 ± 5.