The Structure and Dynamics of Ringed Galaxies. V. The Kinematics of NGC 1512, NGC 3351, NGC 4725, and NGC 4736

The spirals NGC 1512, NGC 3351, NGC 4725, and NGC 4736 are four large nearby examples of ringed galaxies whose kinematic properties are studied in this paper by means of Hα Fabry-Perot interferometry. Velocity fields are first analyzed in terms of pure circular motions, and approximate rotation curves and masses are derived. Then the kinematics of the inner rings alone are studied using a velocity-position angle diagram, and analyzed in terms of circular rotation, rotation plus uniform expansion or contraction, and unperturbed dispersion orbit, or a perturbed oval bar orbit. The results show first that the inner ring in each of these galaxies is a region where Hα emission is enhanced compared with regions inside or outside the ring, and hence that the ring is a zone of active star formation. The pure circular rotation analyses show that in general the kinematic line of nodes does not agree with the position angle of the major axis of the inner ring, suggesting either that the latter is intrinsically oval in shape on average or that expanding/contracting motions are prevalent in rings. Only for NGC 4725 does the velocity-position angle diagram of the inner ring show unmistakable asymmetry indicative of significant noncircular motions. A possible interpretation is that this ring is expanding at 52+/-7 km s^-1^ and rotating at 219+/-4 km s^-1^. However, for all four galaxies models of stable elliptical orbits provide fits to the inner rings which are just as acceptable as pure rotation or expanding/contracting ring fits. In no case is a unique kinematic model of the ring achievable, owing to inadequate knowledge of the parent galaxy orientation parameters.