Can one minor merger explain several prominent Andromeda halo substructures?

Minor-merger simulations investigate a common origin for the Andromeda Giant Southern Stream, Eastern Extent, North-Eastern Shelf and Western Shelf.

Simultaneous Formation of the Andromeda Giant Southern Stream and the Substructures in the Andromeda Halo

Simultaneous Formation of the Andromeda Giant Southern Stream and the Substructures in the Andromeda Halo. Yamaguchi, Misa; Mori, Masao; Kirihara, Takanobu; Miki, Yohei; Ogami, Itsuki; Chiba, Masashi; Komiyama, Yutaka; Tanaka, Mikito, Publications of the Astronomical Society of Japan, 77, L36-L42 (2025).

arXiv:2503.21217 Publication · DOI

Approach

The progenitor dark halo mass and scale radius are varied around expectations from Lambda cold dark matter cosmology, and the resulting debris is compared with the spatial structures in M31.

Main result

A model with a progenitor dark halo mass of 9 billion solar masses and a collision 850 million years ago reproduces the four structures simultaneously within the explored parameter range.

Scientific implications

The unified scenario connects halo debris to the progenitor potential and predicts a companion stream with positive line-of-sight velocity relative to M31. Spectroscopy can test this additional component.

Scope and limitations

The positive-velocity stream and the proposed complete Andromeda Giant Southern Arc remain predictions requiring observational confirmation. The successful scenario is drawn from a limited parameter search.