Title: Optical Spectroscopy and Velocity Dispersions of SZ-selected Galaxy Clusters
Description: We present the design and the first results of a program of optical spectroscopy of galaxies in clusters detected in South Pole Telescope (SPT) data using the Sunyaev-Zel'dovich (SZ) effect, the spectral distortion of the cosmic microwave background from galaxy clusters. We use resampling for an empirical determination of the uncertainty in cluster velocity dispersion calculated from galaxy redshift measurements. We discuss outstanding questions that need answering in order to reach the goal of using cluster velocity dispersion measurements to calibrate scaling relation between the SZ observable and the cluster mass.