How Future Space-Based Weak Lensing Surveys Might Obtain Photometric Redshifts Independently

TL;DR

Adding on-board optical photometric bands to space-based weak lensing instruments significantly enhances galaxy redshift estimation, potentially matching combined space-ground survey performance and reducing dependence on external datasets.

Contribution

This study demonstrates that incorporating optical bands onboard space telescopes can independently achieve high-quality photometric redshifts, improving dark energy parameter constraints.

Findings

Adding U and G bands improves redshift accuracy.

On-board optical bands can match combined space-ground survey results.

Reduces reliance on external ground-based observations.

Abstract

We study how the addition of on-board optical photometric bands to future space-based weak lensing instruments could affect the photometric redshift estimation of galaxies, and hence improve estimations of the dark energy parameters through weak lensing. Basing our study on the current proposed Euclid configuration and using a mock catalog of galaxy observations, various on-board options are tested and compared with the use of ground-based observations from the Large Synoptic Survey Telescope (LSST) and Pan-STARRS. Comparisons are made through the use of the dark energy Figure of Merit, which provides a quantifiable measure of the change in the quality of the scientific results that can be obtained in each scenario. Effects of systematic offsets between LSST and Euclid photometric calibration are also studied. We find that adding two (U and G) or even one (U) on-board optical band-passes to the space-based infrared instrument greatly improves its photometric redshift performance, bringing it close to the level that would be achieved by combining observations from both space-based and ground-based surveys while freeing the space mission from reliance on external datasets.