Dust properties and star formation rates in star-forming dwarf galaxies

We have used the Spitzer Space Telescope to study the dust properties of a sample of star-forming dwarf galaxies. The differences in the mid-infrared spectral energy distributions for these galaxies, which, in general, are low-metallicity systems, indicate differences in the physical properties, heating, and/or distribution of the dust. Specifically, these galaxies have more hot dust and/or very small grains and less PAH emission than either spiral or higher luminosity starburst galaxies. As has been shown in previous studies, there is a gradual decrease in PAH emission as a function of metallicity. Because much of the energy from star formation in galaxies is reradiated in the mid-infrared, star formation rate indicators based on both line and continuum measurements in this wavelength range are coming into more common usage. We show that the variations in the interstellar medium properties of galaxies in our sample, as measured in the mid-infrared, result in over an order of magnitude spread in the computed star formation rates.