Cosmic shear statistics in the Suprime-Cam 2.1 sq deg field: Constraints on Omega_m and sigma_8

TL;DR

This work uses Suprime-Cam RC-band data over 2.1 deg^2 to measure cosmic shear via aperture mass variance and perform a four-parameter maximum likelihood analysis across $\Omega_m$, $\sigma_8$, $\Gamma$, and the mean source redshift $\bar{z}_s$. By decomposing the signal into E- and B-modes and incorporating statistical, systematic, and cosmic-variance uncertainties derived from simulations, the study finds a significant E-mode signal on scales $2'\lesssim \theta_{ap} \lesssim 40'$, but detects a small B-mode at $\theta_{ap} \gtrsim 5'$. The resulting constraints show a degeneracy between $\sigma_8$ and $\bar{z}_s$ and demonstrate that independent information on $\Gamma$ tightens the constraints; for LCDM, they find $0.62<\sigma_8<1.32$ at 95.4% c.l. albeit sensitive to the assumed redshift distribution. The analysis underscores the critical importance of redshift information for robust cosmological inferences from cosmic shear and motivates future, larger, multi-color surveys with mock-calibrated pipelines.

Abstract

We present measurements of the cosmic shear correlation in the shapes of galaxies in the Suprime-Cam 2.1 deg^2 R_c-band imaging data. As an estimator of the shear correlation originated from the gravitational lensing, we adopt the aperture mass variance. We detect a non-zero E mode variance on scales between 2 and 40arcmin. We also detect a small but non-zero B mode variance on scales larger than 5arcmin. We compare the measured E mode variance to the model predictions in CDM cosmologies using maximum likelihood analysis. A four-dimensional space is explored, which examines sigma_8, Omega_m, Gamma and zs (a mean redshift of galaxies). We include three possible sources of error: statistical noise, the cosmic variance estimated using numerical experiments, and a residual systematic effect estimated from the B mode variance. We derive joint constraints on two parameters by marginalizing over the two remaining parameters. We obtain an upper limit of Gamma<0.5 for zs>0.9 (68% confidence). For a prior Gamma\in[0.1,0.4] and zs\in[0.6,1.4], we find sigma_8=(0.50_{-0.16}^{+0.35})Omega_m^{-0.37} for flat cosmologies and sigma_8=(0.51_{-0.16}^{+0.29})Omega_m^{-0.34}$ for open cosmologies (95% confidence). If we take the currently popular LCDM model, we obtain a one-dimensional confidence interval on sigma_8 for the 95.4% level, 0.62<σ_8<1.32 for zs\in[0.6,1.4]. Information on the redshift distribution of galaxies is key to obtaining a correct cosmological constraint. An independent constraint on Gamma from other observations is useful to tighten the constraint.