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 deg 2 in five broad bands (grizy), with a 5 σ point-source depth of r ≈ 26. The Deep layer covers a total of 26 deg 2 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 deg 2). 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.

The Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) is a three-layered imaging survey aimed at addressing some of the most important outstanding questions in astronomy today, including the nature of dark matter and dark energy. The survey has been awarded 300 nights of observing time at the Subaru Telescope, and it started in 2014 March. This paper presents the first public data release of HSC-SSP. This release includes data taken in the first 1.7 yr of observations (61.5 nights), and each of the Wide, Deep, and UltraDeep layers covers about 108, 26, and 4 square degrees down to depths of i ∼ 26.4, ∼26.5, and ∼27.0 mag, respectively (5 σ for point sources). All the layers are observed in five broad bands (grizy), and the Deep and UltraDeep layers are observed in narrow bands as well. We achieve an impressive image quality of 0${^{\prime\prime}_{.}}$6 in the i band in the Wide layer. We show that we achieve 1%–2% point spread function (PSF) photometry (root mean square) both internally and externally (against Pan-STARRS1), and ∼10 mas and 40 mas internal and external astrometric accuracy, respectively. Both the calibrated images and catalogs are made available to the community through dedicated user interfaces and database servers. In addition to the pipeline products, we also provide value-added products such as photometric redshifts and a collection of public spectroscopic redshifts. Detailed descriptions of all the data can be found online. The data release website is https://hsc-release.mtk.nao.ac.jp.

We present the Lyα luminosity functions (LFs) at z = 5.7 and 6.6 derived from a new large sample of 1266 Lyα emitters (LAEs) identified in total areas of 14 and 21 deg2, respectively, based on the early narrowband data of the Subaru/Hyper Suprime-Cam survey. Together with careful Monte Carlo simulations that account for the incompleteness of the LAE selection and the flux estimate systematics in the narrowband imaging, we have determined the Lyα LFs with unprecedentedly small statistical and systematic uncertainties in a wide Lyα luminosity range of 1042.8–43.8 erg s−1. We obtain best-fit Schechter parameters of $L^{*}_{\mathrm{Ly}\alpha } = 1.6^{+2.2}_{-0.6} \ (1.7^{+0.3}_{-0.7}) \times 10^{43}\:\mathrm{erg}\:\mathrm{s}^{-1}$, $\phi ^{*}_{\mathrm{Ly}\alpha } = 0.85^{+1.87}_{-0.77} \ (0.47^{+1.44}_{-0.44}) \times 10^{-4}\:\mathrm{Mpc}^{-3}$, and $\alpha = -2.6^{+0.6}_{-0.4} \ (-2.5^{+0.5}_{-0.5})$ at z = 5.7 (6.6). We confirm that our best-estimate Lyα LFs are consistent with the majority of the previous studies, but find that our Lyα LFs do not agree with the high number densities of LAEs recently claimed by Matthee/Santos et al.’s studies that may overcorrect the incompleteness and the flux systematics. Our Lyα LFs at z = 5.7 and 6.6 show an indication that the faint-end slope is very steep (α ≃ −2.5), although it is also possible that the bright-end LF results are enhanced by systematic effects such as the contribution from AGNs, blended merging galaxies, and/or large ionized bubbles around bright LAEs. Comparing our Lyα LF measurements with four independent reionization models, we estimate the neutral hydrogen fraction of the intergalactic medium to be $x_\mathrm{H\,{\small I}} = 0.3 \pm 0.2$ at z = 6.6, which is consistent with the small Thomson scattering optical depth obtained by Planck 2016.

We present the SILVERRUSH program strategy and clustering properties investigated with ∼ 2, 000 Lyα emitters at z = 5.7 and 6.6 found in the early data of the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey exploiting the carefully designed narrowband filters. We derive angular correlation functions with the unprecedentedly large samples of LAEs at z = 6 − 7 over the large total area of 14 − 21 deg 2 corresponding to 0.3 − 0.5 comoving Gpc 2 . We obtain the average large-scale bias values of b avg = 4.1 ± 0.2 (4.5 ± 0.6) at z = 5.7 (z = 6.6) for > ∼ L * LAEs, indicating the weak evolution of LAE clustering from z = 5.7 to 6.6. We compare the LAE clustering results with two independent theoretical models that suggest an increase of an LAE clustering signal by the patchy ionized bubbles at the epoch of reionization (EoR), and estimate the neutral hydrogen fraction to be x HI = 0.15 +0.15 −0.15 at z = 6.6. Based on the halo occupation distribution models, we find that the > ∼ L * LAEs are hosted by the dark-matter halos with the average mass of log( M h /M ⊙ ) = 11.1 +0.2 −0.4 (10.8 +0.3 −0.5 ) at z = 5.7 (6.6) with a Lyα duty cycle of 1 % or less, where the results of z = 6.6 LAEs may be slightly biased, due to the increase of the clustering signal at the EoR. Our clustering analysis reveals the low-mass nature of > ∼ L * LAEs at z = 6 − 7, and that these LAEs probably evolve into massive super-L * galaxies in the present-day universe.

We investigate Lyα, [Oiii]λ5007, Hα, and [Cii]158µm emission from 1, 124 galaxies at z = 4.9 − 7.0. Our sample is composed of 1, 092 Lyα emitters (LAEs) at z = 4.9, 5.7, 6.6, and 7.0 identified by Subaru/Hyper Suprime-Cam (HSC) narrowband surveys covered by Spitzer large area survey with Subaru/HSC (SPLASH) and 34 galaxies at z = 5.148−7.508 with deep ALMA [Cii]158µm data in the literature. Fluxes of strong rest-frame optical lines of [Oiii] and Hα (Hβ) are constrained by significant excesses found in the SPLASH 3.6 and 4.5 µm photometry. At z = 4.9, we find that the rest-frame Hα equivalent width and the Lyα escape fraction f Lyα positively correlate with the rest-frame Lyα equivalent width EW 0Lyα . The f Lyα − EW 0 Lyα correlation is similarly found at z ∼ 0 − 2, suggesting no evolution of the correlation over z 0 − 5. The typical ionizing photon production efficiency of LAEs is logξ ion /[Hz erg −1 ] 25.5 significantly (60-100%) higher than those of LBGs at a given UV magnitude. At z = 5.7 − 7.0, there exists an interesting turn-over trend that the [Oiii]/Hα flux ratio increases in EW 0 Lyα 0 − 30Å, and then decreases out to EW 0 Lyα 130Å. We also identify an anti-correlation between a [Cii] luminosity to star-formation rate ratio (L [CII] /SF R) and EW 0 Lyα at the > 99% confidence level. We carefully investigate physical origins of the correlations with stellarsynthesis and photoionization models, and find that a simple anti-correlation between EW 0 Lyα and metallicity explains self-consistently all of the correlations of Lyα, Hα, [Oiii]/Hα, and [Cii] identified in our study, indicating detections of metal-poor (∼ 0.03Z ) galaxies with EW 0 Lyα 200Å.