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A.D. Lewis, J.T. Stocke, E. Ellingson (Colorado-CASA)
We present images and 3-color photometry of rich, high-redshift cluster candidates discovered within the sky area of the EMSS. These candidates were X-ray selected using a new technique by Gaidos (1998) which is sensitive to Low Surface Brightness (LSB) objects missed by the EMSS detection method. Cluster candidates were discovered in 10 nights of direct imaging at the 2.1m telescope at Kitt Peak National Observatory. We have analyzed the deep multi-color photometry to provide a rough estimate of the cluster redshifts, comparing each cluster's red sequence of galaxies with empirical galaxy-color models. Using the approximate redshift, we are able to estimate the observed galaxy overdensity, Bgg. Our 3 strongest candidates have estimated redshifts of z~0.3, 0.4 and 0.4, with measured galaxy overdensities equivalent to Abell Class 0, 1 and 3, respectively.
We discuss the hypothesis that these LSB clusters represent a new class of objects which are in the process of formation. Further, the existence of these clusters may imply significant incompleteness in the EMSS sample. We discuss this possibility and its cosmological implications, including evolution in the X-ray Luminosity Function and constraints on \Omegamatter .
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