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J. L. Higdon (Kapteyn Institute), J. F. Wallin (George Mason U.)
We present the first results from a systematic study of the HI morphologies of ring galaxies using the Very Large Array and Australia Telescope Compact Array. Our galaxy sample spans a wide range in ring diameter, star formation rate (SFR), and age to allow a basic investigation of their evolution and star forming properties. The HI rings show a great deal of structure (e.g., holes) regardless of their age or local SFR. Ring nuclei are HI poor in all cases, although molecular gas has been detected in some. Dense HI clumps within the ring boundaries are found only in the youngest systems, and with one possible exception, HI rich ``spokes'' are not found. Only NGC 2793 presents a gas ring embedded in a much larger HI disk, identifying it as a ring galaxy in an early stage of evolution. From the morphologies of the large and evolved systems we conclude that all the rings will eventually contain > 90% of the pre-collision HI that hasn't been splashed out of the disk by the ``intruder''. Starburst activity is clearly associated with the attainment of high HI surface densities (S(HI) > 25 M(solar) pc-2) in the rings, which only occurs in highly evolved systems like AM0644-741 and the Cartwheel. The rearrangement of pre-collision HII regions is probably responsible for most of the H-alpha emission observed in the young objects. Very massive ``intruders'' can severely distort the gas rings in their earliest stages of development, though symmetric and high S(HI) rings may still form in time. Two of the rings in our sample will likely never attain high S(HI) or SFR. But if NGC 2793's ring continues to propagate into its HI disk, it should reach S(HI) ~ 30 M(solar) pc-2 and experience extended starburst activity.
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The author(s) of this abstract have provided an email address for comments about the abstract: jhigdon@astro.rug.nl