The outer low-α disc of the Milky Way – I: evidence for the first pericentric passage of Sagittarius?

Das, Payel; Huang, Yang; Ciucă, Ioana; Fragkoudi, Francesca

Abstract

Phase-space data, chemistry, and ages together reveal a complex structure in the outer low-α disc of the Milky Way. The age-vertical velocity dispersion profiles beyond the Solar Neighbourhood show a jump at 6 Gyr for stars beyond the Galactic plane. Stars older than 6 Gyr are significantly hotter than younger stars. The chemistry and age histograms reveal a bump at [Fe/H] = −0.5, [α/Fe] = 0.1, and an age of 7.2 Gyr in the outer disc. Finally, viewing the stars beyond 13.5 kpc in the age-metallicity plane reveals a faint streak just below this bump, towards lower metallicities at the same age. Given the uncertainty in age, we believe these features are linked and suggest a pericentric passage of a massive satellite ∼6 Gyr ago that heated pre-existing stars, and led to a starburst in existing gas. New stars also formed from the metal-poorer infalling gas. The impulse approximation was used to characterize the interaction with a satellite, finding a mass of ∼1011 M⊙, and a pericentric position between 12 and 16 kpc. The evidence points to an interaction with the Sagittarius dwarf galaxy, likely its first pericentric passage.

Citation

Das, P., Huang, Y., Ciucă, I., & Fragkoudi, F. (2024). The outer low-α disc of the Milky Way – I: evidence for the first pericentric passage of Sagittarius?. Monthly Notices of the Royal Astronomical Society, 527(3), 4505–4514. https://doi.org/10.1093/mnras/stad3344

• Journal Article Type: Article
• Acceptance Date: Oct 27, 2023
• Online Publication Date: Nov 3, 2023
• Publication Date: 2024-01
• Deposit Date: Feb 1, 2024
• Publicly Available Date: Feb 1, 2024
• Print ISSN: 0035-8711
• Publisher: Royal Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 527
• Issue: 3
• Pages: 4505–4514
• DOI: https://doi.org/10.1093/mnras/stad3344
• Public URL: https://durham-repository.worktribe.com/output/2188600
• Publisher URL: https://doi.org/10.1093/mnras/stad3344