Astronomy and Astrophysics – Astrophysics
Scientific paper
Mar 1988
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988apjs...66..233b&link_type=abstract
Astrophysical Journal Supplement Series (ISSN 0067-0049), vol. 66, March 1988, p. 233-259.
Astronomy and Astrophysics
Astrophysics
66
Galactic Structure, Gas Dynamics, Spiral Galaxies, H Ii Regions, Interferometry
Scientific paper
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 H-alpha 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, an 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 H-alpha emission is enhanced compared with regions inside or outside the ring, and hence that the ring is a zone of active star formation. Only for NGC 4725 does the velocity-position angle diagram of the inner ring show an unmistakable asymmetry indicative of significant noncircular motions. 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.
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