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L. J. Kewley (Harvard-Smithsonian Center for Astrophysics), M. A. Dopita (Research School of Astronomy & Astrophysics, ANU), H. A. Smith (Harvard-Smithsonian Center for Astrophysics)
I will present new results in our study of the starburst-AGN connection in the central kiloparsec of merging infrared galaxies. We have developed theoretical optical grids for determining the relative fraction of AGN to starburst emission in active galaxies. These grids have been generated using a combination of detailed stellar population synthesis, photoionization and shock models. The fraction of optical emission associated with AGN versus star formation within the central kiloparsec has been found for each of the mergers in our sample and is compared with indicators of merger evolution, including projected nuclear separation, and a morphological interaction type.
We find that the late mergers in our sample show an unexpected lack of AGN activity (4%), when compared with the AGN activity in both less evolved mergers (30%) and isolated galaxies drawn from the same parent population. These observations appear to contradict the standard merger scenario (Sanders et al. 1988), which predicts increasing AGN activity with merger age. We speculate that our results could be attributed to either;
(1) circumnuclear star formation dominating the optical emission at later stages of the merger, or
(2) hindered AGN feeding, possibly caused by disruption of the accretion disk as a result of the merger.
We acknowledge the support of the Harvard-Smithsonian Center for Astrophysics and the Research School of Astronomy & Astrophysics, Australian National University.
The author(s) of this abstract have provided an email address for comments about the abstract: lkewley@cfa.harvard.edu