The distribution of stellar orbits in eagle galaxies – the effect of mergers, gas accretion, and secular evolution

Santucci, Giulia; Lagos, Claudia Del P; Harborne, Katherine E; Ludlow, Aaron; Proctor, Katy L; Foster, Caroline; McDermid, Richard; Poci, Adriano; Thater, Sabine; van de Ven, Glenn; Zhu, Ling; Walo Martín, Daniel

Abstract

The merger history of a galaxy is thought to be one of the major factors determining its internal dynamics, with galaxies having undergone different types or mergers (e.g. dry, minor, or major mergers) predicted to show different dynamical properties. We study the instantaneous orbital distribution of galaxies in the EAGLE simulation, colouring the orbits of the stellar particles by their stellar age, in order to understand whether stars form in particular orbits (e.g. in a thin or thick disc). We first show that EAGLE reproduces well the observed stellar mass fractions in different stellar orbital families as a function of stellar mass and spin parameter at z = 0. We find that the youngest stars reside in a thin disc component that can extend to the very inner regions of galaxies, and that older stars have warmer orbits, with the oldest ones showing orbits consistent with both hot and counter-rotating classifications, which is consistent with the trend found in the Milky Way and other disc galaxies. We also show that counter-rotating orbits trace galaxy mergers – in particular dry mergers, and that in the absence of mergers, counter-rotating orbits can also be born from highly misaligned gas accretion that leads to star formation.

Citation

Santucci, G., Lagos, C. D. P., Harborne, K. E., Ludlow, A., Proctor, K. L., Foster, C., …Walo Martín, D. (2024). The distribution of stellar orbits in eagle galaxies – the effect of mergers, gas accretion, and secular evolution. Monthly Notices of the Royal Astronomical Society, 528(2), 2326-2345. https://doi.org/10.1093/mnras/stae113

• Journal Article Type: Article
• Acceptance Date: Jan 3, 2024
• Online Publication Date: Jan 11, 2024
• Publication Date: 2024-02
• Deposit Date: Mar 14, 2024
• Publicly Available Date: Mar 14, 2024
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Royal Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 528
• Issue: 2
• Pages: 2326-2345
• DOI: https://doi.org/10.1093/mnras/stae113
• Public URL: https://durham-repository.worktribe.com/output/2329012