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R. Buta, D. A. Crocker, G. G. Byrd (U. Alabama)
We present HST UBVI and ground-based JHK images of ESO 565-11, a barred spiral galaxy recently shown to have a spectacular star-forming nuclear ring (Buta, Purcell, and Crocker 1995, AJ, 110, 1588). The nuclear ring, which is the largest and most intrinsically-elongated example of this type of feature known in any galaxy, was centered in the field of the planetary camera to provide a high-resolution study of its structure. The results provide an interesting picture of the ring and its environment. Dust connected with the ring lies mainly in a symmetric two-armed spiral pattern. More than 500 point sources, mostly unresolved clusters, lie along the ring. Without correcting for internal extinction, the integrated V-band absolute magnitudes of the 10 brightest ring clusters are in the range -12 to -13.6, indicating that they are ``super star clusters'' of the type seen in well-known interacting systems and in other nuclear rings (Barth et al. 1995, AJ, 110, 1009). Evidence for sequential star formation, in the form of a change in orientation of the isophotes of the background starlight with increasing wavelength, suggests the operation of gravity torques on the orbits of aging ring stars. After removing a model of the bulge, the central two arcseconds reveal a one-armed spiral dust arc and an unusual X-shaped pattern. A possible ``microbar'' is seen in the central 0.2 arcseconds radius. The ring is still clearly seen in the JHK images, revealing a knotty appearance indicating that young stars significantly impact its brightness in these passbands. We use these observations to illustrate the morphology and star formation in the vicinity of the likely inner Lindblad resonance in ESO 565-11. The nuclear ring represents an extreme case of linear dimension, intrinsic ellipticity, and degree of star formation in a galaxy with two significant bisymmetric perturbations.
The author(s) of this abstract have provided an email address for comments about the abstract: buta@sarah.astr.ua.edu