UCLA

Ignoring redshift dependence, the statistical performance of a weak lensing survey is set by two numbers: the effective shape noise of the sources, which includes the intrinsic ellipticity dispersion and the measurement noise, and the density of sources that are useful for weak lensing measurements. We provide some general guidance for weak lensing shear measurements from a “generic” space telescope using the galaxy flux signal-to-noise ratio (S/N), ellipticity measurement variance, and effective galaxy number per square degree as metrics to evaluate weak lensing measurement performance across wavelength. Galaxy data are collected from both the ULTRAVISTA field and the Hubble Space Telescope (HST) Frontier Parallel Fields (FPFs) and fitted to radially symmetric Sersic galaxy light profiles. The Sersic galaxy profiles are then stretched to impose an artificial weak lensing shear, and then convolved with a pure Airy Disk PSF to simulate imaging of weak gravitationally lensed galaxies from a hypothetical diffraction-limited space telescope. Our results consistently show that weak lensing measurements are optimized for the longest wavelengths available in the survey, until thermal background from the telescope or interplanetary dust reduces the sensitivity. We also perform a crude measurement of galaxy ellipticities in the HST FPFs using Source Extractor (SExtractor) software (Bertin & Arnouts, 1996) in order to estimate a reduced shear at the location of the parallel fields. The average ellipticity among a significantly large density of distant galaxy images is directly related to reduced gravitational shear signal, which we approximate with our simplifying assumptions and use to estimate the primary FF galaxy cluster masses to illustrate that shear measurements at long NIR wavelengths are completely reasonable.