Speaker
Description
Galaxy cluster abundance measurements provide a classic test of cosmology. However, they exhibit a strong degeneracy between the amplitude of density fluctuations σ8, and the matter density Ωm, as do other similar low-redshift tests such as cosmic shear. The mass distribution in the infall region around galaxy clusters, where material is being accreted from the surrounding field, exhibits an orthogonal cosmological dependence in the Ωm-σ8 plane, making it highly complementary to halo abundance or cosmic shear studies. We explore how weak lensing measurements of the infall region might be used to complement abundance studies, producing forecasts for two weak lensing surveys: UNIONS and Euclid. We then perform this test in practice using UNIONS weak lensing profiles of galaxy clusters in three publicly available catalogues. Comparing profiles from the most complete catalogue to a suite of cosmological simulations with different combinations of Ωm and σ8, we find Ωm = 0.29 +/- 0.05 and σ8 = 0.80 +/- 0.04.
