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Hyper Suprime-Cam (HSC) is a wide-field imaging camera on the prime focus of the 8.2m Subaru telescope on the summit of Maunakea in Hawaii. A team of scientists from Japan, Taiwan and Princeton University is using HSC to carry out a 300-night multi-band imaging survey of the high-latitude sky. The survey includes three layers: the Wide layer will cover 1400 deg2 in five broad bands (grizy), with a 5σ point-source depth of r≈26. The Deep layer covers a total of 26~deg2 in four fields, going roughly a magnitude fainter, while the UltraDeep layer goes almost a magnitude fainter still in two pointings of HSC (a total of 3.5 deg2). Here we describe the instrument, the science goals of the survey, and the survey strategy and data processing. This paper serves as an introduction to a special issue of the Publications of the Astronomical Society of Japan, which includes a large number of technical and scientific papers describing results from the early phases of this survey. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]