Photometric Observations of Star Formation Activity in Early-Type Spiral Galaxies

We observationally study the current star formation activities of early-type spiral galaxies. We construct a complete sample of 15 early-type spiral galaxies having ratios of far-infrared (FIR) to optical B-band luminosity, log (LFIR/LB), larger than average for this type and present CCD imaging of the R and Hα bands. The equivalent widths of Hα emission increase with increasing LFIR/LB, indicating that log (LFIR/LB) can be an indicator of star formation for such early-type spiral galaxies with star formation activities higher than average. For all of the observed early-type spiral galaxies, the extended H II regions exist at the central regions with some asymmetric features. Hα emission is more concentrated to the galactic center than the R-band light, and the degree of the concentration increases with the star formation activity. We also analyze the relation between the star formation activities and the existence of companion galaxies in the sample galaxies and other bright early-type spiral galaxies. No correlation is found; this suggests that the interaction is not responsible for all of the star formation activities of early-type spiral galaxies.