The Once and Future Andromeda Stream
Approach
A forty-million-particle simulation includes self-gravitating disc, bulge and halo components and follows the encounter several billion years forward.
Main result
The stream and eastern and western shells are reproduced. Preserving the observed disc limits the satellite mass to about five billion solar masses in the model.
Scientific implications
Disc survival complements debris morphology as a constraint on the strength of a past merger.
Scope and limitations
The mass bound depends on the assumed encounter and M31 structure. Proposed links to older diffuse arcs are dynamical interpretations, not uniquely established histories.