On the influence of bars and star formation on galactic abundance gradients

Abstract

By means of three-dimensional numerical simulations, we have investigated the influence of gas flows driven by stellar bars and star formation on the abundance gradients in isolated disk galaxies. For axisymmetric disks, the abundance gradients evolve only slightly. The local mechanical energy injection associated with star formation is unable to flatten 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 mixing induced by velocity dispersion. The presence of a bar significantly alters the abundance distribution in both the stellar and the gaseous components. Over most of the galaxy, the slopes of the abundance gradients are reduced in a few dynamical timescales by more than 50%. At a fixed radius, scatter around the mean abundance is found to have two origins, a large-scale variation between arm and interarm regions of about 0.8 dex and an intrinsic, small-scale scatter of ∼ 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 abundance gradients in these regions. Based on these results, we argue that some normal early-type galaxies with flat abundance distributions should either harbor a yet undetected bar or have had one in the past. The results also suggest that these galaxies may contain unusually metal-rich nuclei.