ON THE INFLUENCE OF BARS AND STAR-FORMATION ON GALACTIC ABUNDANCE GRADIENTS

By means of three-dimensional numerical simulations, we have investiga ted the influence of gas flows driven by stellar bars and star formati on on the abundance gradients in isolated disk galaxies. For axisymmet ric disks, the abundance gradients evolve only slightly. The local mec hanical energy injection associated with star formation is unable to f latten the gradient but produces a local abundance scatter of up to 0. 2-0.3 dex in the gas. The stellar abundance gradient is flattened by m ixing induced by velocity dispersion. The presence of a bar significan tly alters the abundance distribution in both the stellar and the gase ous components. Over most of the galaxy, the slopes of the abundance g radients are reduced in a few dynamical timescales by more than 50%. A t a fixed radius, scatter around the mean abundance is found to have t wo origins, a large-scale variation between arm and interarm regions o f about 0.8 dex and an intrinsic, small-scale scatter of approximately 0.4-0.5 dex. On the other hand, central starbursts resulting from the increased fueling of the nucleus by the bar strongly steepen the abun dance gradients in these regions. Based on these results, we argue tha t some normal early-type galaxies with flat abundance distributions sh ould either harbor a yet undetected bar or have had one in the past. T he results also suggest that these galaxies may contain unusually meta l-rich nuclei.