A remarkably high fraction of strong Ly_alpha emitters amongst luminous
  redshift 6.0<z<6.5 Lyman break galaxies in the UKIDSS Ultra-Deep Survey
  We present spectroscopic confirmation of ten highly luminous (L >= 2L*) Lyman
alpha emitters in the redshift range 6.01<z<6.49 (nine galaxies and one AGN),
initially drawn from a sample of fourteen z_phot >= 6 Lyman break galaxies
(LBGs) selected from an area of 0.25 square degrees within the UKIDSS
Ultra-deep Survey (UDS). Overall, our high rate of spectroscopic confirmation
(>= 71%) 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 UV
continuum luminosity we conclude that our sample is consistent with a Ly_alpha
escape fraction of ~25%. Moreover, after careful consideration of the potential
uncertainties and biases, we find that 40%-50% of our sample of L >= 2L*
galaxies at 6.0<z<6.5 display strong Ly_alpha emission (rest-frame equivalent
width >= 25 Angs), a fraction which is a factor of ~2 higher than previously
reported for L <= L* galaxies at z~6. Our results suggest that, as the epoch of
reionization is approached, it is plausible that the Ly_alpha emitter fraction
amongst luminous (L >=2 L*) LBGs shows a similarly sharp increase to that
observed in their lower-luminosity (L <= L*) counterparts.
