The Impact of High-Redshift Galaxy Observations on Weak Lensing Cosmological Constraints

Light from distant galaxies is bent by large-scale structure, and an ensemble statistical analysis of this weak lensing constrains the parameters of the leading cosmological model, ΛCDM. Most weak lensing analyses use observations from comparatively shallow surveys with wide sky coverage; the Dark Energy Survey and Kilo-Degree Survey observed thousands of square degrees but with a depth z<2. We explore cosmological constraints with an alternative paradigm: surveying a small area with extraordinary depth. In particular, we perform a 3x2pt weak lensing analysis of COSMOS-Web, a deep-imaging James Webb Space Telescope treasury program with a narrow 0.6deg² field and galaxy observations out to z=14. Using CosmoSIS for Bayesian inference, we forecast ΛCDM constraints with these observations and investigate the impact of the high redshift catalog. We find that COSMOS-Web strongly constrains S₈ and Ω_M despite its small survey area, and that large area surveys have greater constraining power when combined with COSMOS-Web observations.