The Star Formation Histories of Sculptor Group Dwarf Galaxies. I. Current Star Formation Rates and Oxygen Abundances

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Abstract
We present Hα and [O III] imaging and nebular spectroscopy of H II regions in Sculptor Group dwarf galaxies. Of the eight galaxies in the sample, only two, E471 -006 and A143, have detected H II regions. The H II region luminosity and size distributions for A143 are consistent with those seen in other dwarf galaxies. Electron densities, filling factors and emission measures are similar to those measured in other galaxies at similar distances but vary significantly from compact H II regions in the Magellanic clouds. Oxygen line ratios are used to determine the oxygen abundances and ionization parameters. The oxygen abundances are typically ~0.1 solar and are consistent with the O/H, M_B_ relation. Comparison of the star formation timescales in Sculptor, M81, and Local Groups shows that the higher density M81 Group has many more galaxies forming stars at an above average rate. This is evidence that local galaxy density can have a measurable effect on current star formation. However, a single O/H, M_B_ relation seems to hold for all environments, so galaxy mass still appears to be the primary factor governing a galaxy's chemical evolution.

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