AAS 207th Meeting, 8-12 January 2006
Session 190 Galaxy Clusters at z $>$ 0.5
Oral, Thursday, 10:00-11:30am, January 12, 2006, Maryland

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[190.04] Going to Extremes: The NEP5281 and Cl0023 Clusters at z=0.8

R. R. Gal (University of Virginia), L. M. Lubin (UC Davis), G. K. Squires (Spitzer Science Center)

The process of galaxy cluster formation is well under way at half the current age of the universe. Examining clusters at z~0.8 we find objects at the very extremes of their evolution, from those just coalescing to virialized systems. As part of the High-Redshift Large Scale Structure Survey, we have searched for structure around two systems at z=0.82: the X-ray selected cluster NEP5281, and the optically selected cluster/group Cl0023. Wide-field photometry and multi-object spectroscopy reveal these two systems to be at the opposite ends of the evolutionary spectrum, in both their structure and galaxy content. NEP 5281 appears to be a relaxed system whose galaxies show little or no star formation, whereas Cl0023 consists of numerous merging groups, with extensive ongoing star formation. We discuss the observational results and future prospects for shedding light on galaxy evolution in dense environments.

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