Two major accretion epochs in M31 from two distinct populations of globular clusters

Understand

Large galaxies grow through the accumulation of dwarf galaxies.

• In principle it is possible to trace this growth history using the properties of a galaxy's stellar halo.
• Previous investigations of the galaxy M31 (Andromeda) have shown that outside a radius of 25 kpc the population of halo globular clusters is rotating in alignment with the stellar disk, as are more centrally located clusters.
• The M31 halo also contains coherent stellar substructures, along with a smoothly distributed stellar component.