Appendix from "Gaia-Sausage-Enceladus star formation history as revealed by detailed elemental abundances"

Context. The Gaia-Sausage-Enceladus merger was a major event in the history of the Milky Way. Debris from this merger has been
extensively studied with full kinematic data from the Gaia mission. Understanding the star formation history of the progenitor galaxy
aids in our understanding of the evolution of the Milky Way and galaxy formation in general.
Aims. We aim to constrain the star formation history of the Gaia-Sausage-Enceladus progenitor galaxy using elemental abundances
of member stars. Previous studies on Milky Way satellite dwarf galaxies show that key elemental abundance patterns, which probe
different nucleosynthetic channels, reflect the host galaxy’s star formation history.
Methods. We gather Mg, Fe, Ba, and Eu abundance measurements for Gaia-Sausage-Enceladus stars from the SAGA database.
Gaia-Sausage-Enceladus members are selected kinematically. Inspired by previous studies, we use [Fe/Mg], [Ba/Mg], [Eu/Mg], and
[Eu/Ba], as a function of [Fe/H] to constrain the star formation history of Gaia-Sausage-Enceladus. We use the known star formation
histories and elemental abundance patterns of the Sculptor and Fornax dwarf spheroidal galaxies as comparison.
Results. The elemental abundance ratios of [Fe/Mg], [Ba/Mg], [Eu/Mg], and [Eu/Ba] all increase with [Fe/H] in Gaia-Sausage-
Enceladus. The [Eu/Mg] begins to increase at [Fe/H] ∼ −2.0 and continues steadily, contrasting with the Sculptor dSph galaxy.
The [Eu/Ba] increases and remains high across the [Fe/H] range, contrasting with that of the Sculptor dSph galaxy and deviating
from the Fornax dSph galaxy at high [Fe/H]. The [Ba/Mg] is higher than those of the Sculptor dSph galaxy at the lowest [Fe/H]
and gradually increases, similar to the Fornax dSph galaxy. We constrain three main properties of the Gaia-Sausage-Enceladus star
formation history: 1) star formation started gradually, 2) it extended for over 2 Gyr, and 3) it was quenched around [Fe/H] of −0.5,
likely when it fell into the Milky Way.
Conclusions. We show that the elemental abundance ratios [Fe/Mg], [Ba/Mg], [Eu/Mg], and [Eu/Ba] can be used to trace the star
formation history of a disrupted galaxy when these measurements are available over an [Fe/H] range that is representative of the
progenitor galaxy’s stellar population.