NGC 4314. IV. Photometry of Star Clusters with the [ITAL]Hubble Space Telescope:[/ITAL] History of Star Formation in the Vicinity of a Nuclear Ring

Using HST WFPC2 images, we have obtained U, B, V, I, and H-alpha photometryfor 76 star clusters in the nuclear star-forming ring of the barred spiralgalaxy NGC 4314. These clusters are likely associated with an inner InnerLindblad Resonance, or IILR. The blue colors and H-alpha emission for most ofthese clusters imply very young ages of 1-15 Myr. Age estimates based onseveral reddening-free parameters indicate that the present epoch of starformation has lasted at least 30 Myr. By estimating the masses of stars in theclusters and comparing with the H-alpha luminosity, we conclude that asignificant fraction of ongoing star formation in the nuclear ring of NGC 4314occurs in clusters. The cluster masses identify these as young open clusters,not young globular clusters. Further out in the galaxy, just exterior to thering of young stars, previous ground-based observations revealed two symmetricstellar spiral arms which may be associated with an outer Inner LindbladResonance, or OILR. With our HST data, we have revealed part of this structureand its colors in more detail. The spiral arm colors are consistent withstellar ages between 40 and 200 Myr. The age difference between the inner ringof young stars (IILR) and the larger oval-like feature containing the blue arms(OILR) supports an interpretation of the morphology of the nuclear region ofNGC 4314 that requires a reservoir of gas that becomes more compact over time.We speculate that as the gas distribution becomes more centrally concentrated,it interacts with these two resonances. Each resonance triggers star formation,resulting in two distinct epochs of star formation.