Cosmic variance of weak lensing surveys in the non-Gaussian regime

The results from weak gravitational lensing analyses are subject to a cosmic variance error term that has previously been estimated assuming Gaussian statistics. In this Letter we address the issue of estimating cosmic variance errors for weak lensing surveys in the non-Gaussian regime. Using standard cold dark matter model ray-tracing simulations characterized by Omega(m) = 0.3, Omega(Lambda) = 0.7, h = 0.7 and sigma(8) = 1 for different survey redshifts zs, we determine the variance of the two- point shear correlation function measured across 64 independent lines of sight. We compare the measured variance to the variance expected from a random Gaussian field and derive a redshift- dependent non-Gaussian calibration relation. We find that the ratio between the non-Gaussian and Gaussian variance at 1 arcmin can be as high as similar to 30 for a survey with source redshift z(s) similar to 0.5 and similar to 10 for z(s) similar to 1. The transition scale v(c) above which the ratio is consistent with unity is found to be v(c) similar to 20 arcmin for z(s) similar to 0.5 and v(c) similar to 10 arcmin for z(s) similar to 1. We provide fitting formulae to our results permitting the estimation of non- Gaussian cosmic variance errors, and discuss the impact on current and future surveys. A more extensive set of simulations will, however, be required to investigate the dependence of our results on cosmology, specifically on the amplitude of clustering.