Spiral arms are metal freeways: azimuthal gas-phase metallicity variations in flocculent discs in the FIRE-2 cosmological zoom-in simulations

Creators: Orr, Matthew E.; Burkhart, Blakesley; Wetzel, Andrew; Hopkins, Philip F.; Escala, Ivanna A.; Strom, Allison L.; Goldsmith, Paul F.; Pineda, Jorge L.; Hayward, Christopher C.; Loebman, Sarah R.

Abstract

We examine the azimuthal variations in gas-phase metallicity profiles in simulated Milky Way-mass disc galaxies from the Feedback in Realistic Environments (FIRE-2) cosmological zoom-in simulation suite, which includes a sub-grid turbulent metal mixing model. We produce spatially resolved maps of the discs at z ≈ 0 with pixel sizes ranging from 250 to 750 pc, analogous to modern integral field unit galaxy surveys, mapping the gas-phase metallicities in both the cold and dense gas and the ionized gas correlated with H ɪɪ regions. We report that the spiral arms alternate in a pattern of metal rich and metal poor relative to the median metallicity of the order of ≲0.1 dex, appearing generally in this sample of flocculent spirals. The pattern persists even in a simulation with different strengths of metal mixing, indicating that the pattern emerges from physics above the sub-grid scale. Local enrichment does not appear to be the dominant source of the azimuthal metallicity variations at z ≈ 0: there is no correlation with local star formation on these spatial scales. Rather, the arms are moving radially inwards and outwards relative to each other, carrying their local metallicity gradients with them radially before mixing into the larger-scale interstellar medium. We propose that the arms act as freeways channeling relatively metal poor gas radially inwards, and relatively enriched gas radially outwards.

Additional Information

© 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model) The authors are thankful to the anonymous referee whose comments improved the manuscript. BB is grateful for generous support by the David and Lucile Packard Foundation and Alfred P. Sloan Foundation. AW received support from: NSF via CAREER award AST-2045928 and grant AST-2107772; NASA ATP grant 80NSSC20K0513; HST grants AR-15809, GO-15902, GO-16273 from STScI. The Flatiron Institute is supported by the Simons Foundation. IE acknowledges support from a Carnegie-Princeton Fellowship through the Carnegie Observatories. This research was carried out in part at the Jet Propulsion Laboratory, which is operated by the California Institute of Technology under a contract with the National Aeronautics and Space Administration (80NM0018D0004). We ran simulations using: XSEDE, supported by NSF grant ACI-1548562; Blue Waters, supported by the NSF; Frontera allocations AST21010 and AST20016, supported by the NSF and TACC; Pleiades, via the NASA HEC program through the NAS Division at Ames Research Center. This research has made use of NASA's Astrophysics Data System. DATA AVAILABILITY. The data supporting the plots within this article are available on reasonable request to the corresponding author. A public version of the GIZMO code is available at http://www.tapir.caltech.edu/~phopkins/Site/GIZMO. Additional data including simulation snapshots, initial conditions, and derived data products are available (Wetzel et al. 2022) at http://flathub.flatironinstitute.org/fire.

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