The ages of circumnuclear starbursts from Near-IR spectroscopy: Bushfires or Mexican Wave

We have pbtained K-band spectra with CGS4 on UKIRT for circumnuclear star-forming regions in NGC 4321, NGC 2903 and NGC 7469. A comparison of the equivalent widths of Bry emission and CO absorption with starburst models in the literature allows us to simultaneously determine the age distribution and burst decay timescales around each ring. We find that the majority of the star-forming regions are rapidly decaying bursts with ages between 8 and 10 million years, but that only NGC 4321 displays a clear age sequence. We discuss the implications of these results for the triggering and evolution of circumnuclear star formation.