Weak lensing in the blue: a counter-intuitive strategy for stratospheric observations

Abstract

The statistical power of weak lensing measurements is principally driven by the number of highredshift galaxies whose shapes are resolved. Conventional wisdom and physical intuition suggest this is optimised by deep imaging at long (red or near-IR) wavelengths, to avoid losing redshifted Balmerbreak and Lyman-break galaxies. We use the synthetic Emission Line ('EL')-COSMOS catalogue to simulate lensing observations using different filters, from various altitudes. Here were predict the number of exposures to achieve a target z 0.3 source density, using off-the-shelf and custom filters. Ground-based observations are easily better at red wavelengths, as (more narrowly) are space-based observations. However, we find that SuperBIT, a diffraction-limited observatory operating in the stratosphere, should instead perform its lensing-quality observations at blue wavelengths.