A unified analysis of four cosmic shear surveys

Abstract

In the past few years, several independent collaborations have presented cosmological constraints from tomographic cosmic shear analyses. These analyses differ in many aspects: the datasets, the shear and photometric redshift estimation algorithms, the theory model assumptions, and the inference pipelines. To assess the robustness of the existing cosmic shear results, we present in this paper a unified analysis of four of the recent cosmic shear surveys: the Deep Lens Survey (DLS), the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS), the Science Verification data from the Dark Energy Survey (DES-SV), and the 450 deg 2 release of the Kilo-Degree Survey (KiDS-450). By using a unified pipeline, we show how the cosmological constraints are sensitive to the various details of the pipeline. We identify several analysis choices that can shift the cosmological constraints by a significant fraction of the uncertainties. For our fiducial analysis choice, considering a Gaussian covariance, conservative scale cuts, assuming no baryonic feedback contamination, identical cosmological parameter priors and intrinsic alignment treatments, we find the constraints (mean, 16% and 84% confidence intervals) on the parameter S 8 ≡ σ 8 (Ω m /0.3) 0.5 to be S 8 = 0.94 +0.046 −0.045 (DLS), 0.66 +0.070 −0.071 (CFHTLenS), 0.84 +0.062 −0.061 (DES-SV) and 0.76 +0.048 −0.049 (KiDS-450). From the goodness-of-fit and the Bayesian evidence ratio, we determine that amongst the four surveys, the two more recent surveys, DES-SV and KiDS-450, have acceptable goodness-of-fit and are consistent with each other. The combined constraints are S 8 = 0.79 +0.042 −0.041 , which is in good agreement with the first year of DES cosmic shear results and recent CMB constraints from the Planck satellite. 1936). This effect, known as weak (gravitational) lensing, introduces coherent distortions in galaxy shapes, which carry information of the cosmic composition and history.

Nonparametric cosmology with cosmic shear

“…It is also pointed out in [45], that positive values for the intrinsic alignment parameter, A I , are favored by CFHTLenS. This is the opposite sign to what is expected by theory and could point to lingering systematic effects in the shear catalog.…”

New perspectives on the BOSS small-scale lensing discrepancy for the Planck ΛCDM cosmology

“…Thus, there is significant evidence that the true value for S8 is slightly lower than the Planck18 value of 0.83. But also see Chang et al (2019) for a unified analysis of those 4 shear studies and their reliability. Similarly, Liu et al (2016) provide tentative evidence based on CMB lensing that CFHTLenS shear estimates are systematically too low.…”

Dark Energy Survey year 1 results: Joint analysis of galaxy clustering, galaxy lensing, and CMB lensing two-point functions

“…Systematic errors in these measurements can lead to biased cosmological constraints. As an illustration of these challenges, the recent cross-survey analysis of [12] showed that the cosmological constraints from several recent weak lensing surveys are in tension, and that result from these surveys can be significantly impacted by differences in analysis choices. Distinguishing possible hints of new physics from systematic errors is perhaps the main challenge of present day observational cosmology.…”