The Connection between Bar Strength and Circumnuclear Dust Structure

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