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

We observationally study the current star formation activities of early typespiral galaxies. We construct a complete sample of 15 early type spirals havingfar-infrared (FIR) to optical B band luminosity ratios, L(FIR)/L(B), largerthan the average of the type, and make their CCD imaging of the R and H-alphabands. The equivalent widths of H-alpha emission increase with increasingL(FIR)/L(B), indicating that L(FIR)/L(B) can be an indicator of star formationfor such early type spirals with star formation activities higher than theaverage. For all of the observed early type spirals, the extended HII regionsexist at the central regions with some asymmetric features. H-alpha emission ismore concentrated to the galactic center than the R band light, and the degreeof the concentration increases with the star formation activity. We alsoanalyze the relation between the star formation activities and the existence ofcompanion galaxies in the sample galaxies and other bright early type spirals.No correlation is found and this suggests that the interaction is notresponsible for all of the star formation activities of early type spirals.Comment: LaTex, 23 pages (2 tables included), plus 9 Postscript figures & 1 table. To be published in AJ (November issue