Cosmology from cosmic shear power spectra with Subaru Hyper Suprime-Cam first-year data

Abstract: We measure cosmic weak lensing shear power spectra with the Subaru Hyper Suprime-Cam (HSC) survey first-year shear catalog covering 137deg$^2$ of the sky. Thanks to the high effective galaxy number density of $\sim$17 arcmin$^{-2}$ even after conservative cuts such as magnitude cut of $i<24.5$ and photometric redshift cut of $0.3\leq z \leq 1.5$, we obtain a high significance measurement of the cosmic shear power spectra in 4 tomographic redshift bins, achieving a total signal-to-noise ratio of 16 in the multipole range $300 \leq \ell \leq 1900$. 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 $\Lambda$ cold dark matter ($\Lambda$CDM) model, we find $S_8\equiv \sigma_8(\Omega_{\rm m}/0.3)^\alpha=0.800^{+0.029}_{-0.028}$ for $\alpha=0.45$ ($S_8=0.780^{+0.030}_{-0.033}$ for $\alpha=0.5$) from our HSC tomographic cosmic shear analysis alone. In comparison with Planck cosmic microwave background constraints, our results prefer slightly lower values of $S_8$, 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 in our fiducial cosmic shear analysis, and find that they can shift the best-fit values of $S_8$ by up to $\sim 0.6\sigma$ in both directions. The full HSC survey data will contain several times more area, and will lead to significantly improved cosmological constraints.

• The paper derives cosmic shear power spectra from Subaru HSC first-year data with a signal-to-noise ratio of 16 and an S8 value measured at 0.780+0.030-0.033.
• It employs the pseudo-Cl method to correct survey non-uniformities and accurately separate E- and B-modes, with B-modes remaining consistent with zero.
• Rigorous Bayesian inference incorporates photometric redshift and shape measurement errors, paving the way for tighter cosmological constraints in future surveys.

Analyzing the Implications of Cosmic Shear with Subaru Hyper Suprime-Cam Data

The paper "Cosmology from cosmic shear power spectra with Subaru Hyper Suprime-Cam first-year data" presents findings from the cosmic shear power spectrum analysis using first-year data collected by the Subaru Hyper Suprime-Cam (HSC). This study takes advantage of the significant depth and high image quality of the HSC survey, focusing on a 137 square degree area with an effective source galaxy density after selection cuts.

The primary objective is to derive cosmic shear power spectra that accurately reflect the universe's mass distribution. The authors utilize the pseudo-$C_\ell$ method to correct for survey non-uniformities and assess cosmic shear power spectra across various redshift bins, achieving a total signal-to-noise ratio of 16. Importantly, the study maintains a focus on multipoles within the range of 300 to 1900 to mitigate potential model inaccuracies on smaller scales and circumvent systematic errors such as intrinsic alignments and baryonic feedback.

Key Results and Insights

• The research finds $S_8=0.780^{+0.030}_{-0.033}$, which is slightly lower than the constraints given by the cosmic microwave background (CMB) measurements from the Planck satellite, though the difference is within acceptable uncertainty bounds.
• The cosmic shear power spectra effectively parse into E-modes and B-modes, with the latter providing a consistency check against the null hypothesis. B-modes are found consistent with zero in the fiducial analysis range, reinforcing the methodological robustness of pseudo-$C_\ell$ corrections.
• The study's intrinsic alignment model utilizes a nonlinear alignment paradigm, involving free parameters for alignment amplitude and redshift dependencies, which remain consistent with zero, implying negligible alignment over the scales analyzed.
• Systematic uncertainties from photometric redshift errors and shape measurement biases were rigorously accounted for, with explicit incorporation of various error models within a Bayesian inference framework.

Implications for Future Cosmological Surveys

The results of this study hold significant implications for future cosmic shear analyses. The demonstration that systematic errors and physical model uncertainties like intrinsic alignments and baryonic physics introduce only small biases is encouraging for the use of cosmic shear to constrain cosmological parameters in upcoming weak lensing surveys. Given the expected larger area coverage in future HSC surveys, these results suggest that tighter constraints on cosmological parameters, such as $S_8$ and the dark energy equation of state, may be achievable.

Furthermore, the detailed consistency checks between the HSC findings and CMB constraints suggest that cosmic shear can serve as a complementary probe to other large-scale structure and CMB measurements. When integrated with datasets like Planck's, the HSC data could address current tensions in parameter estimates, such as the discrepancy in $S_8$.

The Subaru Hyper Suprime-Cam's ongoing and future analyses, possessing even greater depth and area, promise enhanced insights into the universe's mass distribution and the cosmic acceleration issue. This paper’s methodology and results pave the way for ambitious synergies with next-generation surveys like the Vera C. Rubin Observatory's LSST and the European Space Agency's Euclid mission.