Star Formation in Galaxies with Large Lower Surface Brightness Disks

We present B, R, and Hα imaging data of 19 large disk galaxies whose properties are intermediate between classical low surface brightness galaxies and ordinary high surface brightness galaxies. We use data taken from the Lowell 1.8m Perkins telescope to determine the galaxies’ overall morphology, color, and star formation properties. Morphologically, the galaxies range from Sb through Irr and include galaxies with and without nuclear bars. The colors of the galaxies vary from B−R = 0.3 – 1.9, and most show at least a slight bluing of the colors with increasing radius. The Hα images of these galaxies show an average star formation rate lower than is found for similar samples with higher surface brightness disks. Additionally, the galaxies studied have both higher gas mass-to-luminosity and diffuse Hα emission than is found in higher surface brightness samples. Subject headings: galaxies: evolution; galaxies: colors; galaxies: luminosities; galaxies: ISM; galaxies: photometry; galaxies: spiral