Skip to main content

Lund University Publications

LUND UNIVERSITY LIBRARIES

Evidence of Gaia Enceladus Experiencing at Least Two Passages around the Milky Way

Skúladóttir, Ása ; Ernandes, Heitor LU ; Feuillet, Diane K. LU orcid ; Mori, Alice ; Feltzing, Sofia LU orcid ; Lucchesi, Romain E.R. and Di Matteo, Paola (2025) In Astrophysical Journal Letters 986(2).
Abstract

One of the major recent breakthroughs has been the discovery of the last major merger to happen in the history of the Milky Way. Around 10 Gyr ago, the galaxy Gaia Enceladus with an estimated ∼10% of the Milky Way mass, fell into the potential of our Galaxy, bringing a large amount of stars that can be identified through their unique chemical and kinematic signatures. Simulations have long predicted that a galaxy of this size should experience several passages through the disk of the Milky Way before eventually being fully dispersed. For the first time, we present observational evidence to support this. We identify two subpopulations accreted from Gaia Enceladus: (1) stars that today have large kinematic energy, which originated from... (More)

One of the major recent breakthroughs has been the discovery of the last major merger to happen in the history of the Milky Way. Around 10 Gyr ago, the galaxy Gaia Enceladus with an estimated ∼10% of the Milky Way mass, fell into the potential of our Galaxy, bringing a large amount of stars that can be identified through their unique chemical and kinematic signatures. Simulations have long predicted that a galaxy of this size should experience several passages through the disk of the Milky Way before eventually being fully dispersed. For the first time, we present observational evidence to support this. We identify two subpopulations accreted from Gaia Enceladus: (1) stars that today have large kinematic energy, which originated from the outskirts of Gaia Enceladus and were accreted during early passages; (2) stars with low kinetic energy accreted at later passages, originating from the inner parts of Gaia Enceladus. Through the use of high-precision chemical abundances, crucially including new aluminum measurements, we show that in all observed abundance ratios ([Fe/H], [Al/Fe], [Mg/Fe], and [Mg/Ba]), stars with high energy show evidence of coming from a less chemically evolved outer region of Gaia Enceladus, compared to the stars with low energy. We therefore conclude that Gaia Enceladus experienced several passages before merging with the main body of our Galaxy. This discovery has wide implications for our understanding of this event and consolidates Gaia Enceladus as a benchmark for studying galaxy mergers and hierarchical galaxy formation in extraordinary detail.

(Less)
Please use this url to cite or link to this publication:
author
; ; ; ; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Astrophysical Journal Letters
volume
986
issue
2
article number
L21
publisher
IOP Publishing
external identifiers
  • scopus:105008817810
ISSN
2041-8205
DOI
10.3847/2041-8213/addc66
language
English
LU publication?
yes
additional info
Publisher Copyright: © 2025. The Author(s). Published by the American Astronomical Society.
id
d02efabc-bf98-4b72-99af-eb8d8bfb0ce0
date added to LUP
2025-12-16 09:41:52
date last changed
2025-12-16 09:42:45
@article{d02efabc-bf98-4b72-99af-eb8d8bfb0ce0,
  abstract     = {{<p>One of the major recent breakthroughs has been the discovery of the last major merger to happen in the history of the Milky Way. Around 10 Gyr ago, the galaxy Gaia Enceladus with an estimated ∼10% of the Milky Way mass, fell into the potential of our Galaxy, bringing a large amount of stars that can be identified through their unique chemical and kinematic signatures. Simulations have long predicted that a galaxy of this size should experience several passages through the disk of the Milky Way before eventually being fully dispersed. For the first time, we present observational evidence to support this. We identify two subpopulations accreted from Gaia Enceladus: (1) stars that today have large kinematic energy, which originated from the outskirts of Gaia Enceladus and were accreted during early passages; (2) stars with low kinetic energy accreted at later passages, originating from the inner parts of Gaia Enceladus. Through the use of high-precision chemical abundances, crucially including new aluminum measurements, we show that in all observed abundance ratios ([Fe/H], [Al/Fe], [Mg/Fe], and [Mg/Ba]), stars with high energy show evidence of coming from a less chemically evolved outer region of Gaia Enceladus, compared to the stars with low energy. We therefore conclude that Gaia Enceladus experienced several passages before merging with the main body of our Galaxy. This discovery has wide implications for our understanding of this event and consolidates Gaia Enceladus as a benchmark for studying galaxy mergers and hierarchical galaxy formation in extraordinary detail.</p>}},
  author       = {{Skúladóttir, Ása and Ernandes, Heitor and Feuillet, Diane K. and Mori, Alice and Feltzing, Sofia and Lucchesi, Romain E.R. and Di Matteo, Paola}},
  issn         = {{2041-8205}},
  language     = {{eng}},
  month        = {{06}},
  number       = {{2}},
  publisher    = {{IOP Publishing}},
  series       = {{Astrophysical Journal Letters}},
  title        = {{Evidence of Gaia Enceladus Experiencing at Least Two Passages around the Milky Way}},
  url          = {{http://dx.doi.org/10.3847/2041-8213/addc66}},
  doi          = {{10.3847/2041-8213/addc66}},
  volume       = {{986}},
  year         = {{2025}},
}