Luminous Compact Blue Galaxies in Intermediate Redshift Galaxy Clusters: A Significant But Extreme Butcher-Oemler Population

We identify a population of Luminous Compact Blue Galaxies (LCBGs) in two galaxy clusters: MS0451.6-0305 (z=0.54) and Cl1604+4304 (z=0.9). LCBGs are identified via photometric characteristics and photometric redshifts derived from broad and narrow band images taken with the WIYN telescope and the Hubble Space Telescope. We analyze their surface densities and clustering properties to find they compose a statistically significant portion (42% and 53%) of the Butcher-Oemler galaxies in both clusters, and their spatial distributions are best characterized by a shell model. The enhancement of the projected space-density of LCBGs with M_B<-18.5 in the clusters relative to the field is 3-10 times higher than the BO population as a whole, but 2 times lower than the red population, except in the core where LCBGs are absent. Assuming some fading, a natural descendant would be small, low-luminosity galaxies found preferentially in today's clusters, such as dEs.