Resolving the Stellar Populations in the Circumnuclear Ring of NGC 7469

We investigate the stellar populations in the star forming ring of theluminous infrared galaxy NGC 7469. We use Hubble Space Telescopemulti-wavelength (UV through NIR) imaging complemented with new K-bandground-based long-slit spectroscopy, and mid-IR and radio maps. Spectral energydistributions (SEDs) and evolutionary synthesis models have been used tocharacterize the star formation at different scales from those of individualstar clusters (tens of pc) to that of the entire star-forming ring (kpc scale).At the smallest scales two different populations of massive (1-10 x 10^6 Msun)clusters are identified. About 25% of the clusters are young (1-3 Myr) andextincted (A_V ~ 3 mag), whereas the vast majority are of intermediate age (~9to 20 Myr) and less obscured (A_V ~ 1 mag). At larger (hundreds of pc) scale,an analysis of the integrated SED and spectroscopic data of the ring indicatesthe presence of two stellar populations. The young (5-6 Myr) and obscuredstellar population accounts for the Br_gamma emission and most of the IRluminosity, and about one-third of the stellar mass of the ring. The much lessobscured intermediate-age population has properties similar to those of themajority of the (older) 1.1um-selected star clusters. These two populations arespatially anti-correlated. The UV-optical-NIR continuum (including the majorityof the clusters) of the ring traces mostly the mildly obscured intermediate-agepopulation, while the MIR and radio peaks mark the location of the youngest andobscured star-forming regions. This study emphasizes the need formulti-wavelength, high-angular resolution observations to characterize the starformation in the dust-obscured regions commonly present in LIRGs.