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

TL;DR

This paper challenges conventional wisdom by showing that stratospheric observations in blue wavelengths can outperform red wavelengths for weak lensing measurements, due to higher source densities at high redshift.

Contribution

It demonstrates through simulations that stratospheric telescopes like SuperBIT should optimize weak lensing observations at blue wavelengths, contrary to traditional approaches.

Findings

Blue wavelength observations yield higher high-redshift galaxy densities.

Stratospheric platforms can outperform ground and space-based red wavelength observations.

Simulations predict fewer exposures needed at blue wavelengths for target source density.

Abstract

The statistical power of weak lensing measurements is principally driven by the number of high redshift 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 Balmer break 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.