Galaxy groups and clusters: Galaxy evolution and cosmology

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Results from large galaxy surveys in the last decade have shown that the formation and evolution of galaxies are intimately tied to the environment around the galaxies, e.g., the local density of galaxies. Galaxy clusters and groups, the largest gravitationaly bound objects in the universe serve as excellent laboratories in learning how the properties and lifetime evolution of galaxies depend on their environment. Furthermore, galaxy clusters, as marker of the highest density regions of the large scale structure in the universe, also provide a way to allow us to constrain the cosmological model of the universe; in particular, by counting their numbers as a function of age in the universe. I have been conducting two of the largest imaging surveys in optical and IR wavelengths to find distant clusters and groups of galaxies, more than two-third way to the edge of the observable universe. The data gathering phase of the surveys has been completed in the last two years. These surveys allow us to discover clusters at the time when the universe was 1/3 the current age, covering a large time line. The large samples of several tens of thousands of galaxy clusters and groups, and more detailed spectroscopic follow-up observations, will allow us, in this proposal, to understand the mechanisms that drive the connections between the environment of galaxies and their evolution in time. We will also discover a large number (about 100) of gravitationally lensed (i.e., magnified) very distant galaxies behind the clusters, which will allow us to study the formation of galaxies when the universe was as young as one and a half billions years old.