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: MS 0451.6 - 0305 (z = 0.54) and Cl 1604 + 4304 (z = 0.9). LCBGs are identified via photometric characteristics and photometric z p 0.54 z p 0.9 redshifts derived from broad- and narrowband images taken with the WIYN telescope and the Hubble Space Telescope (HST). We analyze their surface densities and clustering properties to find that they compose a statistically significant portion (42% and 53%, respectively) of the Butcher-Oemler (BO) galaxies in both clusters and that 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 dE galaxies.