The first-year shear catalog of the Subaru Hyper Suprime-Cam SSP Survey

TL;DR

This paper presents the first-year Subaru/HSC weak-lensing shear catalog, detailing dataset characteristics, the hscPipe-based analysis pipeline, PSF modeling, and corrections for the brighter-fatter effect, coaddition, and bright-object masking. It defines stringent requirements for cosmological weak lensing applications, uses mock catalogs and simulations to quantify covariances and calibrate biases, and performs extensive internal null tests (including PSF-size/shape and star-galaxy correlations) to assess systematics. While PSF model residuals largely meet first-year goals, star–galaxy correlations reveal additive systematics on >1 degree scales that require mitigation in cosmic shear analyses, and photometric redshift uncertainties emerge as a significant systematic in the error budget. The work outlines planned methodological improvements (e.g., multiple shear estimators, metacalibration) and discusses the outlook for early HSC weak-lensing science, including cluster-galaxy lensing and mass mapping, with data products to be publicly released.

Abstract

We present and characterize the catalog of galaxy shape measurements that will be used for cosmological weak lensing measurements in the Wide layer of the first year of the Hyper Suprime-Cam (HSC) survey. The catalog covers an area of 136.9 deg$^2$ split into six fields, with a mean $i$-band seeing of $0.58$ arcsec and $5σ$ point-source depth of $i\sim 26$. Given conservative galaxy selection criteria for first year science, the depth and excellent image quality results in unweighted and weighted source number densities of 24.6 and 21.8 arcmin$^{-2}$, respectively. We define the requirements for cosmological weak lensing science with this catalog, then focus on characterizing potential systematics in the catalog using a series of internal null tests for problems with point-spread function (PSF) modeling, shear estimation, and other aspects of the image processing. We find that the PSF models narrowly meet requirements for weak lensing science with this catalog, with fractional PSF model size residuals of approximately $0.003$ (requirement: 0.004) and the PSF model shape correlation function $ρ_1<3\times 10^{-7}$ (requirement: $4\times 10^{-7}$) at 0.5$^\circ$ scales. A variety of galaxy shape-related null tests are statistically consistent with zero, but star-galaxy shape correlations reveal additive systematics on $>1^\circ$ scales that are sufficiently large as to require mitigation in cosmic shear measurements. Finally, we discuss the dominant systematics and the planned algorithmic changes to reduce them in future data reductions.

Figures (22)

• Figure 1: Map of the $i$-band PSF FWHM across each field. The holes in area coverage are due to masking bright stars, while the other aspects of the area coverage are determined as described in Section \ref{['subsec:area']}.
• Figure 2: Number of exposures contributing to the coadd in the $i$ band across each field. The way exposures are tiled across each survey area results in the repeated pattern of overlap regions with more than the typical number of exposures; see SurveyOverview for discussion of the tiling strategy.
• Figure 3: Unweighted histogram of the $i$-band PSF FWHM values for galaxies in the shear catalog across each field and overall. The vertical dotted line indicates the average PSF FWHM value of $\sim 0.58$${}^{\prime\prime}$.
• Figure 4: $i$-band PSF magnitude distribution of the PSF star sample in each field.
• Figure 5: The average fractional size residual $\langle f_{\delta\sigma}\rangle=\langle (\sigma_{\rm PSF}-\sigma_*)/\sigma_*\rangle$ between PSF stars and PSF models reconstructed at star positions, averaged over the PSF stars within HEALPix pixels with ${\tt NSIDE}=1024$, and shown for each HEALPix pixel as a function of seeing. A symlog scale is used to allow negative residuals to be shown. The dashed line shows the fractional size cut we apply, removing all points above the line and therefore eliminating the cloud of points with large strictly positive $\langle f_{\delta\sigma}\rangle$ values that often but not always have very good seeing. The best-seeing visits in the VVDS region were already removed before production of this figure. Regions with a dark grey background show the linear part of the symlog scale, with the rest being logarithmic.