Satellite group infall into the Milky Way: exploring the Crater-Leo case with new HST proper motions

Understand

Context.

• Within $\Lambda$ Cold Dark Matter ($\Lambda$CDM) simulations, Milky Way-like galaxies accrete some of their satellite galaxies in groups of 3-5 members rather than individually.
• It was also suggested that this might be the reason behind the origin of satellite planes.
• Objects accreted in groups are expected to share similar specific total energy and angular momentum, and also identical orbital planes and directions.