A Hubble Space Telescope optical and ground-based near-infrared study of the giant nuclear ring in ESO 565-11
We present multiband Wide Field Planetary Camera 2 images of the central regions of ESO 565-11, a peculiar southern barred galaxy recently shown to have the largest known example of a circumnuclear starburst ring. We also present ground-based near-infrared H-band imaging and photometry of the galaxy. The results provide an interesting picture of the star-forming ring and its environment. Dust connected with the nuclear ring lies mainly in a symmetric two-armed spiral pattern. More than 700 point sources, mostly unresolved clusters, lie on a highly elliptical ring whose major axis is rotated by more than 20 degrees from that of the isophotes of the background starlight. The luminosity function of these clusters follows a power law with slope a = -2.18 +/- 0.06, typical of young cluster systems. Most of the clusters lie in the age range 4-6 Myr, and most may be metal-rich compared with the Sun. The nuclear ring is still clearly seen in the H band, revealing a knotty appearance indicating that young stars continue to have a significant impact on its brightness in this passband. Numerical simulations are used to show that the nuclear ring of ESO 565-11 has likely formed between two allowed inner Lindblad resonances with the relatively weak primary bar. The results indicate that the excessive size of the ring may be due to an extended hump in the variation of the parameter Omega - kappa/2 with radius. The extreme elongation of the ring and its misalignment with the bar may indicate that it is in an early phase of development. At later times, the simulations suggest that the ring could evolve to a rounder shape. The models do not account for star formation or gas recycling.