Using Action Space Clustering to Constrain the Accretion History of Milky Way like Galaxies

Understand

In the currently favored cosmological paradigm galaxies form hierarchically through the accretion of numerous satellite galaxies.

• Since the satellites are much less massive than the host halo, they occupy a small fraction of the volume in action space defined by the potential of the host halo.
• Since actions are conserved when the potential of the host halo changes adiabatically, stars from an accreted satellite are expected to remain clustered in action space as the host halo evolves.
• In this paper, we identify accreted satellites in three Milky Way like disk galaxies from the cosmological baryonic FIRE-2 simulations by tracking satellite galaxies through simulation snapshots.