We study the extent to which very bright () Lyman-break-selected galaxies at redshifts display detectable Lyα emission. To explore this issue, we obtained follow-up optical spectroscopy of 9 galaxies from a parent sample of 24 galaxy candidates selected from the 1.65 deg2 COSMOS-UltraVISTA and SXDS-UDS survey fields using the latest near-infrared public survey data, and new ultra-deep Subaru z'-band imaging (which we also present and describe in this paper). Our spectroscopy yielded only one possible detection of Lyα at z = 7.168 with a rest-frame equivalent width . The relative weakness of this line, combined with our failure to detect Lyα emission from the other spectroscopic targets, allows us to place a new upper limit on the prevalence of strong Lyα emission at these redshifts. For conservative calculation and to facilitate comparison with previous studies at lower redshifts, we derive a 1σ upper limit on the fraction of UV-bright galaxies at that display , which we estimate to be . This result may indicate a weak trend where the fraction of strong Lyα emitters ceases to rise, and possibly falls between z??6 and . Our results also leave open the possibility that strong Lyα may still be more prevalent in the brightest galaxies in the reionization era than their fainter counterparts. A larger spectroscopic sample of galaxies is required to derive a more reliable constraint on the neutral hydrogen fraction at based on the Lyα fraction in the bright galaxies.
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