Galaxies in the first billion years : implications for reionization and the dtar gormation history at z>6

Redshift 6, one billion years after the Big Bang, marks the end of the reionization epoch. A crucial question is whether the UV flux from young starbursts at this redshift is sufficient to achieve this reionization. We have used the Lyman break technique to identify candidate star-forming galaxies at this redshift in deep HST/ACS images (Stanway et al. 2003; Bunker et al. 2004)