Although nuclear rings and especially nuclear activity have as separate topics received considerable attention in the literature, their possible interrelation has not been much studied. Many nuclear rings, of course, are anecdotally known to occur in galaxies which also host a nuclear starburst or a prominent AGN (often of Seyfert or LINER type, given the typical parameters of the host galaxies involved), and some famous examples include NGC 1068 and NGC 4303.
In a recent paper, we explored the correlations between nuclear activity (both of the non-stellar and starburst variety) and the occurrence of nuclear rings in a sample of 57 nearby spiral galaxies (Knapen 2004b). Using information on the activity from the NASA/IPAC Extragalactic Database (NED) and ring parameters as derived from new H imaging (Knapen et al. 2004b), we found not only that nuclear rings significantly more often than not occur in galaxies which also host nuclear activity (only two of the 12 nuclear rings occur in a galaxy which is neither a starburst nor an AGN host; 30 of the 57 sample galaxies overall would fall into this category), but also that the circumnuclear H emission morphology of the AGN and starbursts is significantly more often in the form of a ring than in non-AGN, non-starburst galaxies (38% of AGN, 33% of starbursts, 11% of non-AGN, and 7% of non-AGN non-starburst galaxies have circumnuclear rings in our sample of galaxies).
Although the number of galaxies in this initial study is rather small for detailed statistical analyses, we did find this most interesting correlation between the occurrence of nuclear rings and that of nuclear activity. Our initial interpretation of this effect is that both nuclear rings, as traced by the massive star formation within them, and starbursts and AGN (of the Seyfert or LINER variety) trace very recent gas inflow. Although it is not clear a priori why the kpc-scale fuelling of nuclear rings and the pc-scale fuelling of activity might be so closely related, nuclear rings do seem to show a potential as tracers of AGN fuelling. These findings may also be related to the reported higher incidence of rings among Seyfert and LINER hosts than among non-AGN galaxies (Arsenault 1989 for nuclear rings; Hunt & Malkan 1999 for inner and outer rings). All these aspects of rings and nuclear activity need further scrutiny.