Transport of Metals in Galactic Disks and Beyond

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The matter in the universe is composed overwhelmingly of hydrogen and helium, which were the only elements made in substantial quantities by the big bang. All the heavier elements, which astronomers refer to generically as "metals," were made by nuclear reactions in the cores of stars, ejected at the ends of the lives of those stars, and then recycled into a next generation of stars and planets. We understand reasonably well how metals are made and ejected from stars, but relatively little about the path they take post-ejection. The goal of this proposal is to greatly improve our knowledge of this process, and thereby to understand the life cycles of the elements that make up our planet and our bodies. The project will involve computer simulations of the flows of metals through and potentially out of the disk of a galaxy. Within the scientific community, the results generated by this project will be of use to people studying both stars and cosmology, and the project itself will help train a new generation of scientists. The broader impact of the work involves a volunteer organization which teaches math and science to inmates in Santa Cruz County Jails.To address the question of how metals are transported through galactic disks, the PI, his collaborators, and students will carry out a campaign of simulations of both isolated shearing boxes and entire galaxies, including a variety of mechanisms for generating instability and transport. They will also conduct simulations of the launching of galactic winds by supernovae, in order to understand how supernova ejecta are or are not mixed with the ambient ISM on their way into a wind. The simulations will use either Athena or PENCIL for the isolated boxes, and ENZO for the whole galaxy and galactic wind calculations. The results of the simulations will be incorporated into a 1D galaxy evolution code in order to study the long-term radial distribution of metals, and both the 1D and full 3D results will be compared with observations. The simulation result will be expressed in the form of parameters (e.g. diffusion coefficients) suitable for other groups to use in semi-analytic models or full cosmological simulations that lack the resolution to model metal diffusion processes self-consistently, and thus must rely on subgrid models. The 1D galaxy evolution code is also open source, and is available for use by the community. The broader impact of the work involves a volunteer organization which teaches math and science to inmates in Santa Cruz County Jails.