A remarkably high fraction of strong Lyα emitters amongst luminous redshift 6.0 < z < 6.5 Lyman-break galaxies in the UKIDSS Ultra-Deep Survey

We present spectroscopic confirmation of 10 highly luminous (L >= 2L*) Ly alpha emitters (LAEs) in the redshift range 6.01 < z < 6.49 (nine galaxies and one active galactic nucleus), initially drawn from a sample of 14 z(phot) >= 6 Lyman-break galaxies (LBGs) selected from an area of 0.25 deg(2) within the UK Infrared Deep Sky Survey (UKIDSS) Ultra-Deep Survey (UDS). Overall, our high rate of spectroscopic confirmation (>= 71 per cent) and low rate of contamination provides a strong vindication of the photometric redshift analysis used to define the original sample. By considering star formation rate estimates based on the Ly alpha and ultraviolet continuum luminosity we conclude that our sample is consistent with a Ly alpha escape fraction of similar or equal to 25 per cent. Moreover, after careful consideration of the potential uncertainties and biases, we find that 40-50 per cent of our sample of L >= 2L* galaxies at 6.0 < z < 6.5 display strong Ly alpha emission (rest-frame equivalent width >= 25 angstrom), a fraction which is a factor of similar or equal to 2 higher than previously reported for L <= L-star galaxies at z similar or equal to 6. Our results suggest that, as the epoch of reionization is approached, it is plausible that the LAE fraction amongst luminous (L >= 2L(star)) LBGs shows a similarly sharp increase to that observed in their lower luminosity (L <= L-star) counterparts.