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The Connection Between Barstrength and Circumnuclear Dust Structure

We present a comparison of barstrength Qb and circumnuclear dust morphology for 75 galaxies in order to investigate how bars affect the centers of galaxies. We trace the circumnuclear dust morphology and amount of dust structure with structure maps generated from visible-wavelength HST data, finding that tightly wound nuclear dust spirals are primarily found in weakly barred galaxies. While strongly barred galaxies sometimes exhibit grand design structure within the central 10 percent of D25, this structure rarely extends to within ~10 pc of the galaxy nucleus. In some galaxies, these spiral arms terminate at a circumnuclear starburst ring. Galaxies with circumnuclear rings are generally more strongly barred than galaxies lacking rings. Within these rings, the dust structure is fairly smooth and usually in the form of a loosely wound spiral. These data demonstrate that multiple nuclear morphologies are possible in the most strongly barred galaxies: chaotic central dust structure inconsistent with a coherent nuclear spiral, a grand design spiral that loses coherence before reaching the nucleus, or a grand design spiral that ends in a circumnuclear ring. These observations may indicate that not all strong bars are equally efficient at fueling material to the centers of their host galaxies. Finally, we investigate the longstanding hypothesis that SB(s) galaxies have weak bars and SB(r) galaxies have strong bars, finding the opposite to be the case: namely, SB(r) galaxies are less strongly barred and have less dust structure than SB(s) galaxies. In general, more strongly barred galaxies tend to have higher nuclear dust contrast.