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R. Buta, P. Treuthardt, D. A. Crocker, G. G. Byrd (U. Alabama)
The early-type barred spiral galaxy NGC 1326 harbors a very bright example of a star-forming nuclear ring, a feature about 1 kpc in diameter located inside the weak bar. From ground-based studies the ring is known to be a strong concentration of H\alpha and radio continuum emission (Garcia-Barreto et al. 1991, RMxAA, 22, 197; Crocker, Baugus, and Buta 1996, ApJS, 150, 353), and from an analysis of the gravitational potential has been shown to lie in the region between two inner Lindblad resonances (Buta et al. 1998, AJ, 116, 1142). We have used the Hubble Space Telescope to image the nuclear ring in six filters (F255W, F336W, F439W, F555W, F656N, and F814W) in order to investigate the star formation in the ring at high resolution. The filters cover the mid-UV, U, B, V, H\alpha, and I-bands, respectively. The observations reveal a ring lined by hundreds of point sources, presumably unresolved clusters, a complex pattern of dust absorption inside, around, and within the ring, and a weak secondary bar or oval. An analysis of the brightest (and likely least extinguished) clusters in the ring reveals very blue colors, consistent with ages of 6± 1 Myr based on the population synthesis models of Bruzual and Charlot (1996, AAS CD-ROM, Vol. 7). However, a comparison between the different filters suggests heavy and variable extinction along the ring: several bright HII regions and HII complexes have little or no counterpart in the broadband images. Our preliminary analysis of the V-band luminosity function indicates the brightest clusters have MV between -10 and -11, which would make them less luminous than the ``super star clusters'' seen in other nuclear rings (e.g., Barth et al. 1995, AJ, 110, 1009; Buta, Crocker, and Byrd 1999, AJ, 118, in press). In this poster, we will present our images, luminosity function, two-color plots, and our judgment of the star formation history of this intriguing structure.
This work is based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract No. NAS5-2655. Support for the analysis of the images was provided by NASA through grant number GO 6496 from the Space Telescope Science Institute, and in part by NSF Grant AST 9617154 to the University of Alabama.