[Paper Review] Hyper Suprime-Cam Year 3 Results: Cosmology from Cosmic Shear Two-point Correlation Functions

Xiangchong Li, Tianqing Zhang+33 more|arXiv (Cornell University)|Apr 3, 2023

Galaxies: Formation, Evolution, Phenomena23 citations

TL;DR

Blinded cosmology analysis of HSC-Y3 cosmic shear 2-point functions yields constraints on Omega_m and S8 within flat LCDM; results are broadly consistent with other HSC analyses but show ~2σ tension with Planck-2018 CMB.

ABSTRACT

We perform a blinded cosmology analysis with cosmic shear two-point correlation functions (2PCFs) measured from more than 25 million galaxies in the Hyper Suprime-Cam three-year shear catalog in four tomographic redshift bins ranging from 0.3 to 1.5. After conservative masking and galaxy selection, the survey covers 416 deg$^2$ of the northern sky with an effective galaxy number density of 15 arcmin$^{-2}$ over the four redshift bins. The 2PCFs adopted for cosmology analysis are measured in the angular range: $7.1 < θ/{ m arcmin} < 56.6$ for $ξ_+$ and $31.2 <θ/{ m arcmin} < 248$ for $ξ_-$, with a total signal-to-noise ratio of 26.6. We apply a conservative, wide, flat prior on the photometric redshift errors on the last two tomographic bins, and the relative magnitudes of the cosmic shear amplitude across four redshift bins allow us to calibrate the photometric redshift errors. With this flat prior on redshift errors, we find $Ω_{ m m}=0.256_{-0.044}^{+0.056}$ and $S_8\equiv σ_8 \sqrt{Ω_{ m m}/0.3}=0.769_{-0.034}^{+0.031}$ (both 68\% CI) for a flat $Λ$ cold dark matter cosmology. We find, after unblinding, that our constraint on $S_8$ is consistent with the Fourier space cosmic shear and the 3$ imes$2pt analyses on the same HSC dataset. We carefully study the potential systematics from astrophysical and systematic model uncertainties in our fiducial analysis using synthetic data, and report no biases (including projection bias in the posterior space) greater than $0.5σ$ in the estimation of $S_8$. Our analysis hints that the mean redshifts of the two highest tomographic bins are higher than initially estimated. In addition, a number of consistency tests are conducted to assess the robustness of our analysis. Comparing our result with Planck-2018 cosmic microwave background observations, we find a ~$2σ$ tension for the $Λ$CDM model.

Motivation & Objective

• Motivate precision cosmology with weak gravitational lensing as a probe of the matter density and clustering amplitude.
• Measure cosmic shear two-point correlation functions from a large, deep imaging survey and calibrate photometric redshift uncertainties.
• Marginalize over a comprehensive set of systematic and modeling uncertainties to obtain robust cosmological constraints.
• Compare results with external probes (Planck, DES, KiDS) and assess consistency and potential tensions.

Proposed method

• Measure real-space cosmic shear two-point correlation functions _+ and _- in four tomographic redshift bins from the HSC-Y3 catalog.
• Model the 2PCFs with a forward model including 23 cosmological, astrophysical, and nuisance parameters.
• Perform a blinded nested Bayesian analysis to constrain cosmological parameters, marginalizing over PSF, shear calibration, photo-z, nonlinear power spectrum, and baryonic physics systematics.
• Calibrate photometric redshift distributions using CAMIRA-LRG cross-correlations and self-calibration techniques in the parameter inference.
• Assess robustness with synthetic data vectors and multiple systematic-model variations, reporting biases 02.5σ in S8.

Experimental results

Research questions

• RQ1 What are the cosmological constraints from cosmic shear 2PCFs in HSC-Y3 under a flat ΛCDM model?
• RQ2 How do systematic uncertainties (PSF modeling, shear calibration, photo-z, nonlinear power spectrum, baryonic physics) propagate into S8 and Ωm constraints?
• RQ3 Are the HSC-Y3 cosmic shear results consistent with Planck-2018 CMB measurements and other lensing surveys (DES, KiDS) within the adopted priors and models?

Key findings

• Ωm = 0.256_{-0.044}^{+0.056} under a flat ΛCDM model.
• S8 = 0.769_{-0.034}^{+0.031} (S8 d arg) when defined as σ8√(Ωm/0.3).
• Constraints are consistent with Fourier-space cosmic shear and 3×2pt analyses on the same HSC dataset after unblinding.
• No biases (including projection bias in posterior space) greater than 0.5σ in the estimation of S8 are found from systematic tests.
• Mean redshift in the two highest tomographic bins may be higher than initial estimates; several internal consistency checks were conducted.