Zabludoff - Abstract Two of the fundamental questions in astronomy today are how structures form in the galaxy distribution and to what extent environment affects galaxy evolution. Surprising results from an on-going survey of five nearby galaxy clusters (Zabludoff et al. 1995) underscore the power of observing clusters of galaxies for data to understand these issues. The research will consist of observations of three unique, carefully chosen samples of clusters of galaxies and smaller groups of galaxies. The results from the observations will be used to, 1) to place stringent constraints on how clusters of galaxies form and on the cosmological mean mass density parameter Omega zero, 2) to isolate the contribution of the cluster environment to galaxy evolution, 3) to determine whether "E+A" galaxies, those strange objects with strong Balmer absorption lines but no line emission, are a link in the chain that connects blue spirals to "SO" galaxies, and 4) to uncover the shape of the faint-end galaxy luminosity function in clusters. Additional results from the reduction and interpretation of the data will include a better understanding of the causes of the Butcher-Oemler effect and of the evolution of the intracluster medium. The results of the observations of the three samples will be used to unravel the detailed evolutionary history of clusters and their galaxies. The results will provide invaluable baselines for future research, when compared with similarly extensive surveys of higher redshift systems underway with the new generation of large ground-based telescopes and NASA satellites . The results from the projects will not only yield answers to the important questions discussed above, but will also be the first and necessary step in the planning of the most extensive survey of nearby clusters and their galaxies ever conceived. Warrick Couch (Ang lo-Australian Observatory and Australia National University), Ian Smail (Carnegie Observatories), and Ann Zabludoff (Carnegie Observatories) are planning to use the Anglo- Australian Telescope's (AAT) 2DF multi-fiber spectrograph, with its 400 fibers, to observe 10,000-20,000 galaxies in approximately 50 rich clusters in a well defined, volume-limited sample. The completion of the 2DF project in the next five years is timed to match the completion of other major redshift surveys of galaxies (Las Campanas, Sloan Digital Sky Survey, and AAT redshift surveys). To understand how all types of galaxies evolve, large statistical surveys like these, which sample comple mentary environments, are needed. The 2DF cluster survey will sample the far tail of the distribution of dense environments, regions which are strongly dependent on the conditions in the early universe and are thus powerful tests of cosmological models. The timing of the 2DF project will also coincide with promising new N-body/hydrodynamic simulations of large-scale structure formation (Evrard, Steinmetz, Lake, and others), with enough dynamic range to include tens of clusters per universe, while maintaining sufficient resolution to monitor the evolution of individual galaxies. For the first time, it will be possible to compare the details of cluster dynamics and cluster galaxy evolution directly with the predictions of theoretical cosmological models. ***
