The Distribution and Properties of H II Regions in Early-to-Intermediate Hubble Type Ringed Galaxies

This paper presents a study of the H II regions in 32 ringed and pseudo-ringed galaxies having Hubble types in the range S0 + to Sc. The objective is to illustrate the distributions of H II regions in classic examples of ringed galaxies and to relate the observed properties to resonance theory. The sample is selected from the Catalog of Southern Ringed Galaxies and includes examples covering a range of ring and galaxy morphological properties. We find that the distribution of Hα luminosity around inner rings is sensitive to the intrinsic shape of the rings. Extremely oval inner rings show a greater concentration of H II regions near the intrinsic ring major axis compared to more circular rings. Nuclear rings are present in several of the sample galaxies and show a range of morphological properties, from a double nuclear ring in NGC 1317 to an irregular feature in NGC 1433. We find also that in galaxies in which an R_1_ outer ring is prominent in the continuum image, the H II regions follow an R^'^_2_ morphology. In several cases, the observed distribution of H II regions strongly supports the idea that the rings are linked to specific orbital resonances with the bar. H II region luminosity functions have been derived for all of the sample galaxies. The functions can be represented by power laws whose exponents are very similar to those found for nonringed galaxies. In a few cases, a luminous nuclear ring produces a secondary peak in the luminosity function. One galaxy shows a break in the luminosity function similar to that observed in other galaxies by Kennicutt, Edgar, & Hodge. The most unusual Hα distribution in the sample was found in the large outer-ringed galaxy NGC 1291. The primary bar, lens, and secondary bar regions of this SO/a galaxy are filled with a wispy pattern of ionized gas filaments very reminiscent of what is seen in the bulge of M31.