The "Building Blocks" of Stellar Halos
  The stellar halos of galaxies encode their accretion histories. In
particular, the median metallicity of a halo is determined primarily by the
mass of the most massive accreted object. We use hydrodynamical cosmological
simulations from the APOSTLE project to study the connection between the
stellar mass, the metallicity distribution, and the stellar age distribution of
a halo and the identity of its most massive progenitor. We find that the
stellar populations in an accreted halo typically resemble the old stellar
populations in a present-day dwarf galaxy with a stellar mass $\sim 0.2-0.5$
dex greater than that of the stellar halo. This suggest that had they not been
accreted, the primary progenitors of stellar halos would have evolved to
resemble typical nearby dwarf irregulars.
