The diverse infrared properties of a complete sample of star-forming dwarf galaxies

We present mid-infrared Spitzer Space Telescope observations of a complete sample of star-forming dwarf galaxies selected from the KPNO International Spectroscopic Survey. The galaxies span a wide range in mid-infrared properties. Contrary to expectations, some of the galaxies emit strongly at 8 mu m, indicating the presence of hot dust and/or PAHs. The ratio of this mid-infrared dust emission to the stellar emission is compared with the galaxies' luminosity, star formation rate, metallicity, and optical reddening. We find that the ratio of the 8.0 mu m dust emission to the stellar emission is more strongly correlated with the star formation rate than it is with the metallicity or the optical reddening in these systems. Nonetheless, there is a correlation between the 8.0 mu m luminosity and metallicity. The slope of this luminosity-metallicity correlation is shallower than corresponding ones in the B band and 3.6 mu m. The precise nature of the 8.0 mu m emission seen in these galaxies (i. e., PAH vs. hot dust or some combination of the two) will require future study, including deep mid-IR spectroscopy.