Galaxy Clusters in the Dark Energy Survey

Abstract

Galaxy clusters are massive dark matter halos, with masses as high as a few times 10^15 M⊙, each hosting tens to hundreds of galaxies. In its first year of data, the Dark Energy Survey has detected more than 100,000 clusters and groups. The upcoming Large Synoptic Survey Telescope is poised to discover over an order of magnitude more. Both of these surveys are well positioned to use galaxy clusters to make leading constraints on cosmological parameters. Two critical components are necessary for a cluster cosmology analysis: measurements of cluster masses, and models of the abundance of dark matter halos. In this thesis I detail two studies on these topics. First, using data from the Dark Energy Survey Year 1 data release, we constrained the masses of redMaPPer clusters using weak lensing. The normalization of the mean mass–richness scaling relation was measured with 5 percent accuracy, the most accurate measurement made to date. Second, as part of the Aemulus Project, using a suite of 40 dark matter only N-body simulations in a multi-dimensional cosmological parameter space, we developed an emulator model that interpolates between these simulations to predict the halo mass function. The mass function emulator achieves better than 1 percent accuracy at mass scales necessary to perform cluster cosmology by using Gaussian Processes to interpolate the results from simulations. This fulfills the stringent requirements of the Large Synoptic Survey Telescope. Finally, I outline ongoing efforts to improve lensing models of galaxy clusters that will enable numerous avenues for performing abundance analyses.