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

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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 zₚhot >= 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 Lyₐlpha and UV continuum luminosity we conclude that our sample is consistent with a Lyₐlpha 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 Lyₐlpha 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 Lyₐlpha emitter fraction amongst luminous (L >=2 L*) LBGs shows a similarly sharp increase to that observed in their lower-luminosity (L <= L*) counterparts.