%0 Generic %1 citeulike:13448973 %A Petit, Antoine C. %A Krumholz, Mark R. %A Goldbaum, Nathan J. %A Forbes, John C. %D 2014 %K imported %T Mixing and transport of metals by gravitational instability-driven turbulence in galactic discs %U http://arxiv.org/abs/1411.7585 %X Metal production in galaxies traces star formation, and is therefore both very patchy and highly concentrated toward the centers of galactic discs. This would seem to suggest that galaxies should have highly inhomogeneous metal distributions with strong radial gradients, but observations of present-day galaxies typically show only shallow gradients with little to no azimuthal variation, implying the existence of a redistribution mechanism. Unfortunately, this mechanism is still poorly understood. We study the possible role of gravitational instability-driven turbulence as a mixing mechanism by simulating an unstable, isolated galactic disc at high resolution, including metal fields treated as passive scalars. Since any cylindrical field can be decomposed into a sum of Fourier-Bessel basis functions, we set up initial metal fields characterized by these functions and study how different modes decay and mix. We find that both shear and turbulence contribute to mixing, but that the mixing rate strongly depends on the symmetries. Non-axisymmetric modes have decay times smaller than the galactic orbital period because shear winds them up to small spatial scales, where they are quickly erased by turbulence. In contrast, the decay timescales for axisymmetric modes are greater than the orbital period of the galaxy, although to all but the largest-scale inhomogeneities the decay time is still short enough for significant mixing to occur over cosmological time. The different timescales provides a natural explanation for why galaxies retain metallicity gradients while there is almost no variation at a fixed radius. Moreover the long timescales required for mixing axisymmetric modes may explain the much greater diversity of metallicity gradients observed in high redshift galaxies compared to local ones. The high-redshift systems have not yet reached equilibrium, while most of the local ones have.

@misc{citeulike:13448973, abstract = {{Metal production in galaxies traces star formation, and is therefore both very patchy and highly concentrated toward the centers of galactic discs. This would seem to suggest that galaxies should have highly inhomogeneous metal distributions with strong radial gradients, but observations of present-day galaxies typically show only shallow gradients with little to no azimuthal variation, implying the existence of a redistribution mechanism. Unfortunately, this mechanism is still poorly understood. We study the possible role of gravitational instability-driven turbulence as a mixing mechanism by simulating an unstable, isolated galactic disc at high resolution, including metal fields treated as passive scalars. Since any cylindrical field can be decomposed into a sum of Fourier-Bessel basis functions, we set up initial metal fields characterized by these functions and study how different modes decay and mix. We find that both shear and turbulence contribute to mixing, but that the mixing rate strongly depends on the symmetries. Non-axisymmetric modes have decay times smaller than the galactic orbital period because shear winds them up to small spatial scales, where they are quickly erased by turbulence. In contrast, the decay timescales for axisymmetric modes are greater than the orbital period of the galaxy, although to all but the largest-scale inhomogeneities the decay time is still short enough for significant mixing to occur over cosmological time. The different timescales provides a natural explanation for why galaxies retain metallicity gradients while there is almost no variation at a fixed radius. Moreover the long timescales required for mixing axisymmetric modes may explain the much greater diversity of metallicity gradients observed in high redshift galaxies compared to local ones. The high-redshift systems have not yet reached equilibrium, while most of the local ones have.}}, added-at = {2019-03-25T08:20:55.000+0100}, archiveprefix = {arXiv}, author = {Petit, Antoine C. and Krumholz, Mark R. and Goldbaum, Nathan J. and Forbes, John C.}, biburl = {https://www.bibsonomy.org/bibtex/28eec7dbccd55bc1c376b3ac1fda09fde/ericblackman}, citeulike-article-id = {13448973}, citeulike-linkout-0 = {http://arxiv.org/abs/1411.7585}, citeulike-linkout-1 = {http://arxiv.org/pdf/1411.7585}, day = 27, eprint = {1411.7585}, interhash = {35afb14c0ddade55a6b6a4a5124fa4bb}, intrahash = {8eec7dbccd55bc1c376b3ac1fda09fde}, keywords = {imported}, month = nov, posted-at = {2014-12-01 05:59:50}, priority = {2}, timestamp = {2019-03-25T08:20:55.000+0100}, title = {{Mixing and transport of metals by gravitational instability-driven turbulence in galactic discs}}, url = {http://arxiv.org/abs/1411.7585}, year = 2014 }