The AGN-Starburst Connection in Infrared Merging Galaxies

I will present new results in our study of the starburst-AGN connection in the central kiloparsec of a large sample of infrared galaxies. We have developed theoretical optical and infrared grids for determining the relative fraction of AGN to starburst emission in composite galaxies. These grids have been generated using a combination of detailed stellar population synthesis, photoionization and shock models. The optical AGN-starburst emission within the central kiloparsec has been found for our sample of merging infrared galaxies and is compared with indicators of merger evolution, including projected nuclear separation, and a morphological interaction type. We find that starburst activity is the dominant emission process in the initial stages of the merger. If an AGN exists, it becomes visible in the optical at intermediate stages of the merger. During the final stages of the merger, starburst activity is the dominant excitation mechanism. These results support an evolutionary scenario in which starburst activity is initially triggered by tidal interactions. As gas is funnelled towards the merger nucleus, an AGN is activated. Towards the final stages of the merger, circumnuclear starburst activity becomes the dominant excitation mechanism rather than the AGN.