We measure cosmic weak lensing shear power spectra with the Subaru Hyper Suprime-Cam (HSC) survey first-year shear catalog covering 137 deg2 of the sky. Thanks to the high effective galaxy number density of ∼17 arcmin−2, even after conservative cuts such as a magnitude cut of i < 24.5 and photometric redshift cut of 0.3 ≤ z ≤ 1.5, we obtain a high-significance measurement of the cosmic shear power spectra in four tomographic redshift bins, achieving a total signal-to-noise ratio of 16 in the multipole range 300 ≤ ℓ ≤ 1900. We carefully account for various uncertainties in our analysis including the intrinsic alignment of galaxies, scatters and biases in photometric redshifts, residual uncertainties in the shear measurement, and modeling of the matter power spectrum. The accuracy of our power spectrum measurement method as well as our analytic model of the covariance matrix are tested against realistic mock shear catalogs. For a flat Λ cold dark matter model, we find $S\,_{8}\equiv \sigma _8(\Omega _{\rm m}/0.3)^\alpha =0.800^{+0.029}_{-0.028}$ for α = 0.45 ($S\,_8=0.780^{+0.030}_{-0.033}$ for α = 0.5) from our HSC tomographic cosmic shear analysis alone. In comparison with Planck cosmic microwave background constraints, our results prefer slightly lower values of S8, although metrics such as the Bayesian evidence ratio test do not show significant evidence for discordance between these results. We study the effect of possible additional systematic errors that are unaccounted for in our fiducial cosmic shear analysis, and find that they can shift the best-fit values of S8 by up to ∼0.6 σ in both directions. The full HSC survey data will contain several times more area, and will lead to significantly improved cosmological constraints.

We investigate photometric properties of Lyman Break Galaxies (LBGs) at z = 3.5 − 5.2 based on large samples of 2,600 LBGs detected in deep (i ′ 27) and wide-field (1,200 arcmin 2 ) images taken in the Subaru Deep Field (SDF) and the Subaru/XMM Deep Field (SXDF) using broad band B, V , R, i ′ , and z ′ filters. The selection criteria for the LBG samples are examined with 85 spectroscopically identified objects, and the completeness and contamination of the samples are estimated from Monte Carlo simulations based on a photometric-redshift catalog of the Hubble Deep Field-North. We find that these LBG samples are nearly rest-frame UV magnitude-limited samples, missing systematically only 10% of red high-z galaxies (in number) which are a dusty population with E(B − V ) 0.4. We calculate luminosity functions of the LBGs with the estimated completeness and contamination, and find (i) that the number density of bright galaxies (M 1700 < −22 ; corresponding to SFR 100h −2 70 M ⊙ yr −1 with extinction correction) decreases significantly from z = 4 to 5 and (ii) that the faint-end slope of the luminosity functions of LBGs may become steeper towards higher redshifts. We estimate dust extinction of z ≃ 4 LBGs with M < M * (≃ −21) from UV-continuum slopes, and obtain E(B − V ) = 0.15 ± 0.03 as the mean value. The dust extinction remains constant with apparent luminosity, but increases with intrinsic (i.e., extinction-corrected) luminosity. We find no evolution in dust extinction between LBGs at z = 3 and 4. We investigate the evolution of UV-luminosity density by integrating the luminosity functions of LBGs, and find that the UV-luminosity density at 1700Å, ρ UV does not significantly change from z = 3 to z = 5, i.e., ρ UV (z = 4)/ρ UV (z = 3) = 1.0 ± 0.2 and ρ UV (z = 5)/ρ UV (z = 3) = 0.8 ± 0.4, thus the cosmic star-formation rate (SFR) density (with correction for dust extinction) remains constant within the error bars, or possibly a slight decline, from z = 3 to z = 5. We estimate the stellar mass density from the cosmic SFR thus obtained, and find that this stellar mass density is consistent with those derived directly from the stellar mass function at z = 0 − 1, but exceeds those at z ∼ 3 by a factor of 3. We find that the ratio of the UV-luminosity density of Lyman α emitters (LAEs) to that of LBGs is ≃ 60% at z ≃ 5, and thus about a half of star formation probably occurs in LAEs at z ≃ 5. We obtain a constraint on the escape fraction of UV-ionizing photons (i.e., UV continuum in 900Å) produced by LBGs, f esc 0.13. This implies that the escape fraction of LBGs may be larger than that of star-forming galaxies at z = 0.

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.

We have built an 80-mega pixels (10240×8192) mosaic CCD camera, called Suprime-Cam, for the widefield prime focus of the 8.2 m Subaru telescope. Suprime-Cam covers a field of view 34'×27', a unique facility among the the 8-10 m class telescopes, with a resolution of 0."202 per pixel. The focal plane consists of ten high-resistivity 2k×4k CCDs developed by MIT Lincoln Laboratory, which are cooled by a large stirling-cycle cooler. The CCD readout electronics was designed to be scalable, which allows the multiple read-out of tens of CCDs. It takes 50 seconds to readout entire arrays. We designed a filter-exchange mechanism of the jukebox type that can hold up to ten large filters (205 × 170 × 15 mm 3 ). The wide-field corrector is basically a three-lens Wynne-type, but has a new type of atmospheric dispersion corrector. The corrector provides a flat focal plane and an un-vignetted field of view of 30' in diameter. The achieved co-planarity of the focal array mosaic is smaller than 30 µm peak-to-peak, which realizes mostly the seeing limited image over the entire field. The median seeing in the I c -band, measured over one year and a half, is 0."61. The PSF anisotropy in Suprime-Cam images, estimated by stellar ellipticities, is about 2% under this median seeing condition. At the time of commissioning, Suprime-Cam had the largest survey speed, which is defined as the field of view multiplied by the primary mirror area of the telescope, among those cameras built for sub-arcsecond imaging.