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C. L. Martin (STScI), J. Lotz (JHU), H. C. Ferguson (STScI)
The star formation history of dwarf galaxies has a significant impact on the interpretation of deep galaxy counts, the faint-end slope of the luminosity function, and the metal content of the intergalactic and intracluster media. At least in local clusters of galaxies, where catalogs are complete to absolute magnitudes of roughly -14, dwarf elliptical galaxies are the most numerous type of galaxy. A significant subset of both the Virgo dE's and the structurally-similar dwarf spheroidals in our Local Group experienced major episodes of star formation only a few billion years ago. It is currently unclear whether environmental factors or starburst-driven winds control the bursting cycle. We have begun searching for the star-forming progenitors of the dwarf elliptical population and hope to directly measure the clustering properties and star formation rates of the progenitors. Even in moderate-redshift clusters any population of dwarf galaxies is greatly out-numbered by background field galaxies at similar apparent magnitude. We present very deep narrow-band images of two redshift 0.4 clusters. The filters were carefully chosen to isolate [OII] emission in the fast, prime-focus beam of the KPNO Mayall 4m telescope. We present candidates for a previously undetected population of dwarf emission-line galaxies. These candidates are not strongly clustered and are below the detection limits of most spectroscopic surveys.