Abstract

A number of recent studies have found evidence for a tension between observations of large-scale structure (LSS) and the predictions of the standard model of cosmology with the cosmological parameters fit to the cosmic microwave background (CMB). The origin of this ‘S8 tension’ remains unclear, but possibilities include new physics beyond the standard model, unaccounted for systematic errors in the observational measurements and/or uncertainties in the role that baryons play. In this talk, I will examine the latter possibility using the new FLAMINGO suite of large-volume cosmological hydrodynamical simulations. I will discuss how important ‘feedback’ processes that affect the baryons are implemented and calibrated in the simulations and how the simulations are projected onto observable space for comparisons with observational measurements of cosmic shear, CMB lensing, and the thermal Sunyaev-Zel’dovich (tSZ) effect. I will then focus on the dependence of the predictions on the efficiency and nature of baryonic feedback and whether or not it can plausibly resolve the S8 tension. Finally, I will discuss some independent tests that the simulations can be subjected to in order to build confidence (or undermine it!) in our cosmological conclusions.