The properties of the nuclei of the two hot SPOT galaxies NGC 1097 and 2997.

Abstract

NGC 1097 and 2997 are barred-spiral galaxies with hot spots in annuli around their central red nuclei. IUE low-dispersion spectra of two hot spots in NGC 1097 and of the ensemble of knots in the annulus around the central nucleus of NGC 2997 are presented. In addition, low-dispersion visible spectra of the hot spots and nuclei of both galaxies are analyzed, and near-infrared photometry has been obtained. Both galaxies show UV spectral features of early B supergiants together with A giants. In the optical and near-infrared, the addition of K giants is indicated. The lack of O stars in the UV and the deduced high extinction of the ionized regions favor clumps with cores of obscured O stars. In NGC 2997, the mass in early-type stars in each spot is similar to that of 30 Doradus, whilst for the knots in NGC 1097 the mass is a factor about 10 times larger than for 30 Dor. However, the largest clumps in these galaxies are still a factor of a few times less massive than those observed in irregular Markarian galaxies.