# Grad Talk- Enhancing optical galaxy cluster cosmology with multiwavelength follow up of a small, complete cluster sample

Matt Kirby, University of Arizona

Abstract:  Galaxy clusters are the largest gravitationally collapsed objects in the universe and trace the highest peaks in the matter density field. By measuring their abundances, we can place constraints on cosmological parameters, namely the matter density, $Omega_M$, and a measure of the matter clustering, $\sigma_8$. The precision to which we can perform this measurement is currently dominated by the uncertainty of the richness--mass relation, the expected number of galaxies in a cluster as a function of its mass. Using follow-up observations of the richest clusters in a cosmological sample (both the Sloan Digital Sky Survey and the Dark Energy Survey), I have tightened the constraints on the scatter in the richness--mass relation which translates to tighter cosmological constraints. I will begin by introducing the methods we use to extract cosmology from galaxy cluster abundances and follow with my work using multiwavelength (X-ray and mm-wave) follow-up data of the richest clusters to improve the precision of cluster cosmology measurements.

** Refreshments served from 2:45pm – 3:00pm in PAS 218. Please join us for the colloquium in PAS 224. Thank you. **

## When

2 p.m. to 3 p.m. Feb. 14, 2020

PAS 218

Carmen Montijo