CSST WL preparation I: forecast the impact from non-Gaussian covariances and requirements on systematics control

The precise estimation of the statistical errors and accurate removal of the systematical errors are the two major challenges for the stage IV cosmic shear surveys. We explore their impact for the China Space Station Telescope (CSST) with survey area ${\sim} 17\,500\deg ^2$ up to redshift ~4. We consider statistical error contributed from Gaussian covariance, connected non-Gaussian covariance, and super-sample covariance. We find the non-Gaussian covariances, which is dominated by the super-sample covariance, can largely reduce the signal-to-noise ratio of the two-point statistics for CSST, leading to an ~1/3 loss in the figure of merit for the matter clustering properties (σ₈-Ω_m plane) and 1/6 in the dark energy equation of state (w₀-w_a plane). We further put requirements of systematics mitigation on intrinsic alignment of galaxies, baryonic feedback, shear multiplicative bias, and bias in the redshift distribution, for an unbiased cosmology. The 10^-2-10^-3 level requirements emphasize strong needs in related studies, to support future model selections and the associated priors for the nuisance parameters.