Spurious shear in weak lensing with the Large Synoptic Survey Telescope

The complete 10-yr survey from the Large Synoptic Survey Telescope (LSST) will image ∼20 000 deg2 of the sky in six filter bands every few nights, bringing the final survey depth to r ∼ 27.5, with over four billion well-measured galaxies. To take full advantage of this unprecedented statistical power, the systematic errors associated with weak lensing measurements need to be controlled to a level similar to the statistical errors. This work is the first attempt to quantitatively estimate the absolute level and statistical properties of the systematic errors on weak lensing shear measurements due to the most important physical effects in the LSST system via high-fidelity ray-tracing simulations. We identify and isolate the different sources of algorithm-independent, additive systematic errors on shear measurements for LSST and predict their impact on the final cosmic shear measurements using conventional weak lensing analysis techniques. We find that the main source of the errors comes from an inability to adequately characterize the atmospheric point spread function due to its high-frequency spatial variation on angular scales smaller than ∼10 arcmin in the single short exposures, which propagates into a spurious shear correlation function at the 10−4-10−3 level on these scales. With the large multi-epoch data set that will be acquired by LSST, the stochastic errors average out, bringing the final spurious shear correlation function to a level very close to the statistical errors. Our results imply that the cosmological constraints from LSST will not be severely limited by these algorithm-independent, additive systematic effects.