Very weak lensing in the CFHTLS Wide: Cosmology from cosmic shear in the linear regime

TL;DR

This paper uses CFHTLS T0003 Wide data to constrain the amplitude of the matter power spectrum through cosmic shear in the linear regime, covering 57 deg^2 with i' ≤ 24.5. It employs a robust weak-lensing pipeline (KSB+ with STEP calibration), a detailed redshift distribution from Deep fields, and a careful covariance treatment including non-Gaussian corrections, enabling cosmological inferences from large-scale, linear scales up to 85 Mpc. The authors obtain consistent constraints on Ω_m and σ_8 across multiple shear statistics, with σ_8(Ω_m/0.25)^{0.64}=0.785±0.043 for the full angular range, and, when combined with WMAP3, Ω_m=0.248±0.019 and σ_8=0.771±0.029. They demonstrate that linear-regime cosmic shear provides competitive cosmological constraints, validate the methodology against systematics, and highlight the potential of future large-area surveys to exploit linear scales for precision cosmology.

Abstract

We present an exploration of weak lensing by large-scale structure in the linear regime, using the third-year (T0003) CFHTLS Wide data release. Our results place tight constraints on the scaling of the amplitude of the matter power spectrum sigma_8 with the matter density Omega_m. Spanning 57 square degrees to i'_AB = 24.5 over three independent fields, the unprecedented contiguous area of this survey permits high signal-to-noise measurements of two-point shear statistics from 1 arcmin to 4 degrees. Understanding systematic errors in our analysis is vital in interpreting the results. We therefore demonstrate the percent-level accuracy of our method using STEP simulations, an E/B-mode decomposition of the data, and the star-galaxy cross correlation function. We also present a thorough analysis of the galaxy redshift distribution using redshift data from the CFHTLS T0003 Deep fields that probe the same spatial regions as the Wide fields. We find sigma_8(Omega_m/0.25)^0.64 = 0.785+-0.043 using the aperture-mass statistic for the full range of angular scales for an assumed flat cosmology, in excellent agreement with WMAP3 constraints. The largest physical scale probed by our analysis is 85 Mpc, assuming a mean redshift of lenses of 0.5 and a LCDM cosmology. This allows for the first time to constrain cosmology using only cosmic shear measurements in the linear regime. Using only angular scales theta> 85 arcmin, we find sigma_8(Omega_m/0.25)_lin^0.53 = 0.837+-0.084, which agree with the results from our full analysis. Combining our results with data from WMAP3, we find Omega_m=0.248+-0.019 and sigma_8 = 0.771+-0.029.

Figures (16)

• Figure 1: Sky coverage of the W1, W2 and W3 fields used in this work. Each CCD is drawn as a small rectangle and each MegaCam field is a squared mosaic of 36 rectangles. The small white holes are regions with missing data.
• Figure 2: The pattern of the PSF anisotropy in an example pointing ${\rm W}3+2+0-{\rm CFHTLS\_W}\_i\_143023+543031$. Ticks represent the observed ellipticities at stellar locations. On top of the figure a 10% ellipticity modulus is shown for comparison.
• Figure 3: The average galaxy weight (with arbitrary normalisation) as a function of $i'_{AB}$ in the range of [21.5;24.5].
• Figure 4: Two-point statistics from the combined 57 pointings. The error bars of the E-mode include statistical noise added in quadrature to the non-Gaussian cosmic variance. Only statistical uncertainty contributes to the error budget for the B-mode. Red filled points show the E-mode, black open points the B-mode. The enlargements in each panel show the signal in the angular range $35\arcmin$-$230\arcmin$.
• Figure 5: The top-hat E-mode shear signals of W1 up to $200\arcmin$, of W2 up to $120\arcmin$ and of W3 up to $230\arcmin$ are shown. The error bars includes statistical noise and cosmic variance for each individual field.