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J. M. Lotz (Johns Hopkins University), C. L. Martin (California Institute of Technology), H. C. Ferguson (STScI)
We present the results of our [OII] 3727Å\ emission line search for star-bursting progenitors of dwarf elliptical galaxies and compare the star-forming dwarf galaxy populations of two intermediate redshift clusters, Cl0939+4713 (z=0.41) and MS1512.4+3647 (z=0.37). Dwarf elliptical galaxies are the most common type of galaxy in nearby clusters, yet their star formation histories and evolution are poorly understood. The star formation history of dwarf galaxies has a significant impact on the interpretation of deep galaxy counts, the faint-end slope of the galaxy luminosity function, and the metal content of intergalactic gas. Many of the Local Group dwarf spheroidals and dwarf ellipticals have had complex star formation histories, with one or more bursts of star formation 1-8 Gyr ago after an initial star formation period \ge 10 Gyr ago. It is unclear whether these starburst periods and subsequent gas loss are internally regulated via supernova-driven winds or externally produced via environmental effects such as tidal interactions or galaxy harassment. We have begun searching for the progenitors to dwarf elliptical galaxies at intermediate redshift and have obtained KPNO 4-meter deep narrow-band (centered on the redshifted [OII] 3727Å\ emission line) images of Cl0939+4713 and MS1512.4+3647 clusters. Combined with deep broad-band imaging, we are able to identify star-forming dwarf galaxy cluster candidates, constrain their star formation rates at z ~ 0.4, and compare the star-forming dwarf populations of the two clusters.