Pixelation Effects in Weak Lensing

Weak gravitational lensing is a promising probe of dark matter and darkenergy requiring accurate measurement of the shapes of faint, distant galaxies.Such measures are hindered by the finite resolution and pixel scale of typicalcameras. On the other hand, as imaging telescopes are practically limited to afixed number of pixels and operational life-span, so the survey area increaseswith pixel size. We investigate the optimum choice of pixel scale in thistrade-off for a space-based mission, using the full engineering model andsurvey strategy of the proposed SuperNova/Acceleration Probe as an example. Ourmethodology is to simulate realistic astronomical images of known shear and toevaluate the surface density of sources where the shear is accurately recoveredusing the Rhodes, Refregier, & Groth algorithm in the context of the deriveddark matter power spectrum. In addition to considering single exposures, wealso examine the benefits of sub-pixel dithering. Although some of our resultsdepend upon the adopted shape measurement method, the relative trends,particularly those involving the surface density of resolved galaxies, arerobust. Our approach provides a practical counterpart to studies which considerthe effects of pixelation from analytic principles, which necessarily assume anidealized shape measurement method. We find that the statistical error on themass power spectrum is minimized with a pixel scale equal to 75-80% of the FWHMof the point-spread function, and that dithering is marginally beneficial atlarger pixel scales.Comment: 17 pages, 12 figures, submitted for publication to PAS