Ring Star Formation Rates in Barred and Nonbarred Galaxies
  Nonbarred ringed galaxies are relatively normal galaxies showing bright rings
of star formation in spite of lacking a strong bar. This morphology is
interesting because it is generally accepted that a typical ring forms when
material collects near a resonance, set up by the pattern speed of a bar or
bar-like perturbation. Our goal in this paper is to examine whether the ring
star formation properties are related to the non-axisymmetric gravity potential
in general. For this purpose, we obtained H{\alpha} emission line images and
calculated the line fluxes and star formation rates (SFRs) for 16 nonbarred SA
galaxies and four weakly barred SAB galaxies with rings. For comparison, we
combine our observations with a re-analysis of previously published data on
five SA, seven SAB, and 15 SB galaxies with rings, three of which are
duplicates from our sample. With these data, we examine what role a bar may
play in the star formation process in rings. Compared to barred ringed
galaxies, we find that the inner ring SFRs and H{\alpha}+[N ii] equivalent
widths in nonbarred ringed galaxies show a similar range and trend with
absolute blue magnitude, revised Hubble type, and other parameters. On the
whole, the star formation properties of inner rings, excluding the distribution
of H ii regions, are independent of the ring shapes and the bar strength in our
small samples. We confirm that the deprojected axis ratios of inner rings
correlate with maximum relative gravitational force Q_g; however, if we
consider all rings, a better correlation is found when local bar forcing at the
radius of the ring, Q_r, is used. Individual cases are described and other
correlations are discussed. By studying the physical properties of these
galaxies, we hope to gain a better understanding of their placement in the
scheme of the Hubble sequence and how they formed rings without the driving
force of a bar.
