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S. Sakai (UCLA), R.C. Kennicutt (Steward Observatory), C. Moss (Liverpool John Moore University)
We present a progress report on a H\alpha imaging survey of nearby clusters of galaxies. The broad goals of the survey are: (1) to construct a complete inventory of star forming galaxies in a well-defined volume limited sample, (2) to characterize the demographics of the local star forming population, and (3) to quantify the completeness of other methods for measuring the local SFR density. With the Mosaic CCD Imager on the 0.92m telescope at KPNO, we are able to cover an 1\circ field in a single observation, and reach limiting fluxes corresponding to star formation rates of about 0.1 M\odot/yr for extended galaxies and ~0.01 M\odot/yr for compact emission-line galaxies. During three separate runs, we have observed 25 1-degree fields in eight clusters: A262, A347, A400, A426, A569, A779, A1367 and A1656. We have also obtained follow-up spectroscopy for some galaxies, in order to confirm their cluster membership, using the Lick 3m telescope.
A preliminary comparison of H\alpha luminosity functions obtained from our imaging survey with those from the prism survey reveals a significant level of incompleteness in the latter. This in turn is due to a combination of insensitivity to low-luminosity emission-line galaxies and to brighter galaxies with weak extended H\alpha emission. The survey has also revealed a unique population of clustered dwarf emission-line objects which may be the results of recent tidal encounters between larger gas-rich galaxies.