Fall 2023 Physics Colloquium: Measuring cosmology with optical galaxy clusters

Abstract: Galaxy clusters are embedded in the most massive bound structures in the Universe. These structures formed from gravitationally amplified peaks in the primordial matter distribution making their properties sensitive to cosmology. In the standard approach the abundances of clusters as a function of their mass are used to constrain cosmology. Because cluster masses cannot be measured directly this approach relies on observable proxies of cluster mass that are calibrated using weak gravitational lensing. Robustly marginalizing over these mass-observable relations is therefore critical to accurately measuring cosmology with clusters. Recently, data from clusters identified in the Dark Energy Survey (DES) were found to be in significant tension with a variety of other probes, including a 5.6-sigma tension with cosmic microwave background data. This tension was likely caused by incomplete modeling of the impact of cluster selection. We have developed a novel framework to forward model cluster selection in cosmological simulations to address this discrepancy. When applied to the same DES cluster data we have found that this framework can consistently describe the DES cluster data assuming a Planck cosmology, thereby resolving the tension observed in earlier analyses of the DES cluster data.

In-person only - Refreshments in PAS 218, 2:30PM