Building up the Stellar Halo of the Milky Way
  We study numerical simulations of satellite galaxy disruption in a potential resembling that of the Milky Way. Our goal is to assess whether a merger origin for the stellar halo would leave observable fossil structure in the phase-space distribution of nearby stars. We show how mixing of disrupted satellites can be quantified using a coarse-grained entropy. Although after 10 billion years few obvious asymmetries remain in the distribution of particles in configuration space, strong correlations are still present in velocity space. We briefly describe how we can understand these effects based on the conservation of fine-grained phase-space density in an action-angle formalism. We also discuss the implications of our results on the known properties of the stellar halo. 
Amina Helmi (Sterrewacht Leiden) and Simon D.M. White (MPA, Garching)