Detection of correlated galaxy ellipticities on CFHT data: first evidence for gravitational lensing by large-scale structures

TL;DR

This paper reports the first detection of gravitational lensing effects caused by large-scale structures through galaxy ellipticity correlations in CFHT data, confirming theoretical predictions and demonstrating the feasibility of weak lensing surveys for cosmology.

Contribution

It presents the first significant detection of cosmic shear from galaxy ellipticity correlations using CFHT data, validating weak lensing as a tool for studying dark matter and cosmology.

Findings

Detected a 5.5 sigma excess of galaxy ellipticity correlations.

Measured correlation amplitude of 2.2% at 1 arcmin, consistent with predictions.

Data favor cluster-normalized cosmological models, marginally rejecting some CDM models.

Abstract

We report the detection of a significant (5.5 sigma) excess of correlations between galaxy ellipticities at scales ranging from 0.5 to 3.5 arc-minutes. This detection of a gravitational lensing signal by large-scale structure was made using a composite high quality imaging survey of 6300 arcmin^2 obtained at the Canada France Hawaii Telescope (CFHT) with the UH8K and CFH12K panoramic CCD cameras. The amplitude of the excess correlation is 2.2\pm 0.2 % at 1 arcmin scale, in agreement with theoretical predictions of the lensing effect induced by large-scale structure.We provide a quantitative analysis of systematics which could contribute to the signal and show that the net effect is small and can be corrected for. We show that the measured ellipticity correlations behave as expected for a gravitational shear signal. The relatively small size of our survey precludes tight constraints on cosmological models. However the data are in favor of cluster normalized cosmological models, and marginally reject Cold Dark Matter models with (Omega=0.3, sigma_8<0.6) or (Omega=1, sigma_8=1). The detection of cosmic shear demonstrates the technical feasibility of using weak lensing surveys to measure dark matter clustering and the potential for cosmological parameter measurements, in particular with upcoming wide field CCD cameras.