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

Abstract

We observationally study the current star formation activities of early type spiral galaxies. We construct a complete sample of 15 early type spirals having far-infrared (FIR) to optical B band luminosity ratios, log(L FIR /L B ), larger than the average of the type, and make their CCD imaging of the R and Hα bands. The equivalent widths of Hα emission increase with increasing L FIR /L B , indicating that log(L FIR /L B ) can be an indicator of star formation for such early type spirals with star formation activities higher than the average. For all of the observed early type spirals, 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 spirals. No correlation is found and this suggests that the interaction is not responsible for all of the star formation activities of early type spirals.

An Imaging Survey of Early‐Type Barred Galaxies

“…Figure 9: This is a known starburst galaxy (e.g., Devereux 1989;Usui, Saitō , & Tomita 1998). The roundness of the outer isophotes and the low H i width (W 50 ¼ 182 km s À1 ) reported by Theureau et al (1998) both indicate the galaxy is close to face-on; the position angle for the outer disk is rather uncertain.…”

“…Fortunately, the H i mapping performed by van Driel & van Woerden (1991) yields plausible values of 50 for both inclination and position angle for the two outer rings, where most of the H i is concentrated. We assume these rings to be coplanar with the stellar disk.…”

“…The color map shows that the inner ring surrounding the bar is blue; Usui et al (1998) noted H emission from this ring and Verheijen & Sancisi (2001) indicate that most of the galaxy's H i is in the ring as well. Inside, there are several strong dust lanes.…”

“…Numerous patchy blue spiral arms form a partial inner pseudo-ring around the bar. These arms are almost certainly sites of recent or ongoing star formation; Usui et al (1998) traced the '' inner ring '' in H emission. The dust lanes are stronger on the S side, suggesting that side of the galaxy is nearer.…”

The nuclear and extended infrared emission of the Seyfert galaxy NGC 2992 and the interacting system Arp 245

“…This inclined spiral galaxy (b/a=0.31;de Vaucouleurs et al 1991) is located at a luminosity distance of 36.6 Mpc and it is part of the interacting system Arp 245. This system is formed by NGC 2992, the spiral star-forming galaxy NGC 2993 (Usui, Saito, & Tomita 1998) and the tidal dwarf galaxy Arp 245 North (hereafter Arp 245N; Duc et al 2000). Two bright tidal features connect these three galaxies, suggesting that the system is in an early stage of the interation (Duc et al 2000).…”