The ratio of [Eu/$α$] differentiates accreted/in-situ Milky Way stars across metallicities, as indicated by both field stars and globular clusters
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| Main Authors: | , , , , , , , , , |
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| Format: | Preprint |
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2024
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| author | Monty, Stephanie Belokurov, Vasily Sanders, Jason L. Hansen, Terese T. Sakari, Charli M. McKenzie, Madeleine Myeong, GyuChul Davies, Ellot Y. Ardern-Arentsen, Anke Massari, Davide |
| author_facet | Monty, Stephanie Belokurov, Vasily Sanders, Jason L. Hansen, Terese T. Sakari, Charli M. McKenzie, Madeleine Myeong, GyuChul Davies, Ellot Y. Ardern-Arentsen, Anke Massari, Davide |
| contents | We combine stellar orbits with the abundances of the heavy, $r$-process element europium and the light, $α$-element, silicon to separate in-situ and accreted populations in the Milky Way across all metallicities. At high orbital energy, the accretion-dominated halo shows elevated values of [Eu/Si], while at lower energies, where many of the stars were born in-situ, the levels of [Eu/Si] are lower. These systematically different levels of [Eu/Si] in the MW and the accreted halo imply that the scatter in [Eu/$α$] within a single galaxy is smaller than previously thought. At the lowest metallicities, we find that both accreted and in-situ populations trend down in [Eu/Si], consistent with enrichment via neutron star mergers. Through compiling a large dataset of abundances for 46 globular clusters (GCs), we show that differences in [Eu/Si] extend to populations of in-situ/accreted GCs. We interpret this consistency as evidence that in $r$-process elements, GCs trace the star formation history of their hosts, motivating their use as sub-Gyr timers of galactic evolution. Furthermore, fitting the trends in [Eu/Si] using a simple galactic chemical evolution model, we find that differences in [Eu/Si] between accreted and in-situ MW field stars cannot be explained through star formation efficiency alone. Finally, we show that the use of [Eu/Si] as a chemical tag between GCs and their host galaxies extends beyond the Local Group, to the halo of M31 - potentially offering the opportunity to do Galactic Archaeology in an external galaxy. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2405_08963 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | The ratio of [Eu/$α$] differentiates accreted/in-situ Milky Way stars across metallicities, as indicated by both field stars and globular clusters Monty, Stephanie Belokurov, Vasily Sanders, Jason L. Hansen, Terese T. Sakari, Charli M. McKenzie, Madeleine Myeong, GyuChul Davies, Ellot Y. Ardern-Arentsen, Anke Massari, Davide Astrophysics of Galaxies Solar and Stellar Astrophysics We combine stellar orbits with the abundances of the heavy, $r$-process element europium and the light, $α$-element, silicon to separate in-situ and accreted populations in the Milky Way across all metallicities. At high orbital energy, the accretion-dominated halo shows elevated values of [Eu/Si], while at lower energies, where many of the stars were born in-situ, the levels of [Eu/Si] are lower. These systematically different levels of [Eu/Si] in the MW and the accreted halo imply that the scatter in [Eu/$α$] within a single galaxy is smaller than previously thought. At the lowest metallicities, we find that both accreted and in-situ populations trend down in [Eu/Si], consistent with enrichment via neutron star mergers. Through compiling a large dataset of abundances for 46 globular clusters (GCs), we show that differences in [Eu/Si] extend to populations of in-situ/accreted GCs. We interpret this consistency as evidence that in $r$-process elements, GCs trace the star formation history of their hosts, motivating their use as sub-Gyr timers of galactic evolution. Furthermore, fitting the trends in [Eu/Si] using a simple galactic chemical evolution model, we find that differences in [Eu/Si] between accreted and in-situ MW field stars cannot be explained through star formation efficiency alone. Finally, we show that the use of [Eu/Si] as a chemical tag between GCs and their host galaxies extends beyond the Local Group, to the halo of M31 - potentially offering the opportunity to do Galactic Archaeology in an external galaxy. |
| title | The ratio of [Eu/$α$] differentiates accreted/in-situ Milky Way stars across metallicities, as indicated by both field stars and globular clusters |
| topic | Astrophysics of Galaxies Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2405.08963 |