This project centers on optical (visible-light) observations using large, ground-based telescopes, designed to maximally exploit the science return from the South Pole Telescope (SPT). The SPT, an NSF-funded experiment at the Amundsen-Scott South Pole Station, consists of a 10-meter diameter, millimeter-wave radio telescope designed to measure the subtle fluctuations in the brightness of the cosmic background radiation (CBR) at multiple wavelengths. As part of its survey operations, the SPT is producing a list of possible galaxy clusters detected by the effect the hot, intra-cluster plasma has on the CBR. The size of this spectral distortion, known as the Sunyaev-Zel'dovich (SZ) effect, is independent of distance, offering the opportunity to inventory galaxy clusters in the universe, relatively free of the strong distance bias that affects other types of observations. In this project the collaborating team (from Smithsonian Astrophysical Observatory and Harvard University) will perform optical follow-up observations of the SPT cluster candidates, to confirm the existence of the clusters, to obtain their redshifts, and to identify the member galaxies. The team will make use of an array of existing instrumentation on the current suite of large telescopes, including PISCO, a multi-bandpass imaging camera developed with NSF support for the 6.5-meter Magellan telescope. The primary result of this work will be an unprecedented, volume-limited catalog of approximately 600 galaxy clusters. The full catalog of photometric and spectroscopic observations will be released to the astronomical community through a web-accessible archive using well-developed database architectures. These observations are intended to enable a wide variety of subsequent inquiries, including studies of galaxy evolution in different environments, efforts to further constrain cosmological parameters, and cluster mass measurements through gravitational lensing. The project will support the work of a postdoctoral fellow, as well as graduate and undergraduate students, and will be publicized through the Principal Investigators' close involvement with significant public-media projects.
