"The Lyman Continuum Escape Fraction of z>3 Galaxies in the CANDELS Fields"

The Reionization of the Universe is one of the most important and hottest topics of the present day astrophysical research. The most plausible candidates for the reionization process are star-forming galaxies, which according to the predictions of the majority of the theoretical and semi-analytical models should dominate the HI ionizing background at z>3. We have used deep U-band imaging in the COSMOS, CANDELS GOODS-NORTH, and EGS fields in order to estimate the Lyman continuum escape fraction of 69 star forming galaxies at z~3 down to faint magnitude limits (L=0.2L*). We have measured a stringent upper limit (<2%) for the escape fraction of HI ionizing photons from bright galaxies (L>L*), while for the faint population (L=0.2L*) the limit to the escape fraction is <10%. We have computed their contribution to the observed UV background at z~3 and we have found that it is difficult to keep the Universe ionized at z~3 only with star-forming galaxies. We compare our results with recent achievements on the Lyman continuum escape fraction of high-z galaxies and AGN in the literature and discuss future prospects to shed light on the Dark Ages.