Cosmology from Cosmic Shear with DES Science Verification Data

TL;DR

This paper presents initial cosmological constraints from the Dark Energy Survey's weak lensing data, demonstrating the potential of cosmic shear measurements for understanding dark energy and matter distribution.

Contribution

First constraints on cosmology from DES weak lensing data using cosmic shear, with analysis of systematics and comparison to other datasets.

Findings

Measured $\sigma_8 (\Omega_m/0.3)^{0.5} = 0.81 \pm 0.06$ from DES SV data.

Results are stable against data vector and systematics choices.

Constraints are consistent with Planck and mildly discrepant with CFHTLenS.

Abstract

We present the first constraints on cosmology from the Dark Energy Survey (DES), using weak lensing measurements from the preliminary Science Verification (SV) data. We use 139 square degrees of SV data, which is less than 3\% of the full DES survey area. Using cosmic shear 2-point measurements over three redshift bins we find $\sigma_8 (\Omega_{\rm m}/0.3)^{0.5} = 0.81 \pm 0.06$ (68\% confidence), after marginalising over 7 systematics parameters and 3 other cosmological parameters. We examine the robustness of our results to the choice of data vector and systematics assumed, and find them to be stable. About $20$\% of our error bar comes from marginalising over shear and photometric redshift calibration uncertainties. The current state-of-the-art cosmic shear measurements from CFHTLenS are mildly discrepant with the cosmological constraints from Planck CMB data; our results are consistent with both datasets. Our uncertainties are $\sim$30\% larger than those from CFHTLenS when we carry out a comparable analysis of the two datasets, which we attribute largely to the lower number density of our shear catalogue. We investigate constraints on dark energy and find that, with this small fraction of the full survey, the DES SV constraints make negligible impact on the Planck constraints. The moderate disagreement between the CFHTLenS and Planck values of $\sigma_8 (\Omega_{\rm m}/0.3)^{0.5}$ is present regardless of the value of $w$.