The distinct stellar metallicity populations of simulated Local Group
  dwarfs
  A number of Local Group dwarf galaxies are known to have two spatially
segregated stellar metallicity populations, a centrally concentrated metal-rich
population and a more extended metal-poor population. In this work we discuss
mechanisms that lead to the formation of two spatially segregated metallicity
populations. Using a set of high-resolution hydrodynamical simulations of Local
Group-like environments, we select a sample of satellite and field galaxies,
spanning the stellar mass range $10^6-10^9$M$_{\odot}$, that exhibit bimodality
in their metallicity distributions. Among those, we identify a subsample with a
strong spatial segregation in the two populations. We find three distinct
mechanisms for their formation. In field dwarfs and in a small fraction of
satellites, a merger causes the metal-poor stars to migrate to larger radii and
encourages the available gas to sink to the centre of the dwarf. Most of the
gas is subsequently blown out of the halo through star formation feedback, but
the remaining gas is consumed in the formation of a metal-rich population. In
the exclusive case of satellites that have retained some of their gas at
infall, it is the compression of this gas by ram pressure near pericentre that
triggers the formation of metal-rich stars, whilst simultaneously preventing
star formation at larger radii through stripping. Additionally, in a small
number of field and satellite dwarfs, interactions with gaseous filaments and
other galaxies can result in the formation of a metal-rich population.
Regardless of the formation mechanism, a history of mergers typically enhances
the spatial segregation.
