CONSTRAINING THE RELATION BETWEEN CLUSTER VELOCITY DISPERSION AND RICHNESS USING THE REDMAPPER YEAR 3 CATALOG
Physical and Biological Sciences
Physics (Astrophysics)
In this thesis we examine the correlation between galaxy cluster velocity dispersion and richness, which is a measure of number density. This study was conducted using the redMaPPer Year 3 cluster and member catalogs produced by the Dark Energy Survey. We used spectroscopic redshifts to measure the galaxy velocity dispersions of galaxy clusters which is indicative of a galaxy cluster's mass. We analyzed 62 clusters containing at least 15 member galaxies with spectroscopic measurements using the biweight scale estimator and the gapper method to establish their velocity dispersions. Confidence intervals were determined using bootstrap resampling with replacement. We fit power laws between our velocity dispersions and richness using the Kelly method. By comparing these two methods of obtaining velocity dispersions it appears that the gapper method is more stable for this study. With further research we hope to compare our results with other mass-richness relations established using gravitational lensing or X-ray emission, and shed light on the intrinsic scatter of this relation. Using this methodology, with expanded spectroscopic surveys, will refine the use of the observable richness as a proxy for cluster mass. By better understanding the masses of galaxy clusters we may be able to better understand Dark Energy and its role in the evolution of the Universe.
