Assigned ID: 670 ----- Attempting Submission 1 (Fri Feb 25 21:33:37 GMT 2011) ----- The error eppars to be that the abstract is more than 20 lines, while it is 18... Not clear why it complaints. Some `composite' Seyfert 2 nuclei show evidence for massive ultra-compact starbursts within the central 40-200 pc. When spatially resolved with the HST, these starbursts exhibit morphology similar to `canonical,' 1-2 kpc size, nuclear rings which form as a result of radial gas inflows in barred and (maybe) interacting galaxies. Based on our recent work, although only a few of such Ultra-Compact Nuclear Rings (UCNRs) are known to date, there are reasons to believe that this is the tip of the iceberg. UCNRs can be closely related to both the AGN and starburst activity in the nucleus, and to the host galaxy. They may thus be the missing link between the two. We propose the first comprehensive statistical study of the fraction and properties of such UCNRs in nearby galaxies using HST archival data. We shall also investigate the UCNR population in matched samples of Seyfert 2s, LINERs, `transition' objects and `pure' nuclear starbursts. The targets will be selected from the homogeneous survey of 486 objects of Ho et al., of which we estimate more than half to have suitable archive data. We shall find the size, ellipticity, color distributions and stellar populations of the UCNRs, explore how they relate to nuclear activity and analyze correlations between UCNR population and global galactic properties. We shall determine whether the UCNRs form a distinct population from the canonical 1-2 kpc size nuclear rings or they constitute the tail distribution of their larger counterparts. The properties of the UCNR population will allow us to distinguish between the various theoretical models of gas flow within the central 40-200 pc, thus providing stringent clues to the fueling mechanisms of AGN and explore any possible linkage between central starbursts and AGN. While we do not expect to provide definitive answers to all of these questions, this will be the first attempt to link observationally and theoretically the AGN processes to those in their host galaxies.

UNRESOLVED STELLAR POPULATIONS AND GALAXY STRUCTURE 12 Medium false 0.0 0.0 false false false false SUPPORTED