NGC 3115 and the nature of SO disks

Imaging observations of the edge-on SO galaxy NGC 3115 have been obtained with a scanning CCD in three bandpasses and with the 4-Shooter. A comparison of photometry derived from these frames with previous measurements shows satisfactory agreement. Models have been generated for the bulge and disk components to permit the determination of their colors. It is found that in the B - i color the disk is 0.50 mag bluer than the bulge. Also, spiral arms are apparent in the 4-Shooter frames, and these arms are significantly bluer than the interarm region of the disk. This color difference is much larger than is expected for a typical SO galaxy, and suggests that NGC 3115 was undergoing star formation until quite recently. This is difficult to reconcile with the very large bulge-to-disk ratio derived here and in other studies. The combination of no neutral hydrogen and a global spiral pattern further complicates the interpretation. 41 refs.