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Session 66 - Galaxies.
Display session, Thursday, June 11
Using HST WFPC2 images, we have derived U, B, V, I, and H-alpha photometry for 80 star clusters in the nuclear star-forming ring in the barred spiral galaxy NGC 4314. The blue colors and strong H-alpha emission for some of these clusters imply very young ages of less than 5 Myr. Further out in the galaxy, just exterior to this ring of young stars, previous ground-based observations revealed an oval-shaped ring with bluer colors than the bar or nucleus. With our HST data, we have further investigated this structure by fitting and subtracting nested ellipses to the isophotal contours, revealing this structure and its colors in more detail. These colors are consistent with stellar ages between 100 and 300 Myrs. The age progression between the inner ring of young stars and the larger oval-like feature suggests a shrinking ring of star formation. Alternatively, these two structures may be associated with resonances driven by a nuclear bar.
We model these images with power-law radial profiles, and show that the luminosity densities in the inner core are very high. At r = 5 pc (for D = 10 Mpc), the luminosity densities are in excess of 5000 L_\sun pc^-3. Such high central surface brightnesses may imply the existence of a massive compact central object.
We acknowledge NASA Grant NAG5-1603 and the support of the HST Astrometry Science Team (W. Jefferys, P. Shelus, P. Hemenway, W. van Altena, L. Fredrick, O. Franz, and R. Duncombe).
Program listing for Thursday