Identify the progenitor of the early dynamical perturbation

Identify the dwarf-galaxy progenitor responsible for the substantial dynamical perturbation of the Milky Way’s high-alpha disk at a lookback time of approximately 10.8–11.5 Gyr, including whether it was an early passage of Gaia–Sausage–Enceladus.

Background

The paper infers that the age distribution of the younger Splash component records a substantial dynamical perturbation of the early high-alpha disk approximately 10.8–11.5 Gyr ago. Within the merger-heating scenario, this event scattered stars born in the disk onto low-angular-momentum, halo-like orbits.

The responsible progenitor is not identified. The authors discuss an early pericentric passage of Gaia–Sausage–Enceladus as one possibility, while noting that the progenitor remains uncertain. Resolving its identity would clarify the early merger history of the Milky Way disk.

References

The perturbation may have been driven by the accretion and merger of a dwarf galaxy, although the responsible progenitor remains uncertain.

— The Milky Way's Early Disk Was Built in Bursts. I. Evidence from Low-angular-momentum, High-$α$ Stars Scattered Out of the Protodisk by Merger Events  (2610.26374 - Sun et al., 19 Oct 2026) in Section 3, “Implications for the early merger history”