Circumnuclear star formation in the early-type resonance ring barred spiral galaxy NGC 1326

Abstract

We present multiband WFPC2 images of the nuclear ring of NGC 1326, an early-type southern barred spiral in the nearby Fornax galaxy cluster. The ring is a typical example of a 1 kpc-sized star-forming ring located in the region of the inner Lindblad resonances with the weak primary bar. The images reveal nearly 1000 point sources in and around the ring. Those sources brighter than M-v = -9 are probably massive young clusters, while the fainter sources may include a mix of extremely luminous stars and fainter clusters. From an analysis of reddening-free parameters and two-color plots, we find evidence for a spread in ages of ring clusters, from less than 5 Myr to at least 200 Myr. The older clusters still lie within the nuclear ring, with no evidence of migration of the ring being found over this time period. The luminosity function reveals no clusters having an (uncorrected) absolute magnitude M-v brighter than -11, and even after correction for extinction the most luminous cluster identified has only M-v(0) = -12.6. The ring seems to lack the "super-star clusters" (SSCs) seen in starburst systems and in other nuclear rings, and the analysis suggests that SSCs are not a universal property of these rings. Complex dust structure is found inside the ring, south of the nucleus, and extinction is especially severe on the west side of the ring. An H alpha image reveals hundreds of H II regions and emission complexes in the nuclear ring, but there is little correlation between these H II regions and the observed continuum sources, most likely owing to reddening and age differences in the ring.