Life in the Outer Limits: Insights on Hierarchical Assembly from Stellar Halos in the Local Universe

Owing to their large dynamical timescales, the stellar haloes of Milky Way (MW) sized galaxies represent ideal environments to test modern theories of galaxy formation within the Lambda-CDM paradigm. Only in stellar haloes can the remnants of hierarchical accretion both be preserved over long timescales as in-tact dwarf satellites or as tidal debris and be easily distinguished from the underlying smooth structure. Stellar haloes, however, remain some of the most difficult galactic structures to study due to their large angular extent (to Rvirial) and extremely low surface brightness (>30 mag/square arcsec). Thus, the basic properties of stellar haloes -- the overall stellar distribution, substructure fraction, global kinematics and detailed stellar content -- remain relatively unconstrained.

Three studies are presented in this work. The first revisits the discovery of subgiants in the early 20th century. The second is a detailed study of the stellar halo of the Andromeda Galaxy. The third is a deep probe of the minor merger in NGC5387.

Note: Several figures are intentionally degraded in the primary PDF to reduce the file size. Full EPS files for these figures are included as supplementary material.