A "Universal" Density Profile for the Outer Stellar Halos of Galaxies
  The outer stellar halos of galaxies contain vital information about the
formation history of galaxies, since the relaxation timescales in the outskirts
are long enough to keep the memory, while the information about individual
formation events in the central parts has long been lost due to mixing, star
formation and relaxation. To unveil some of the information encoded in these
faint outer halo regions, we study the stellar outskirts of galaxies selected
from a fully hydrodynamical high resolution cosmological simulation, called
Magneticum. We find that the density profiles of the outer stellar halos of
galaxies over a broad mass range can be well described by an Einasto profile.
For a fixed total mass range, the free parameters of the Einasto fits are
closely correlated. Galaxies which had more (dry) merger events tend to have
lesser curved outer stellar halos, however, we find no indication that the
amount of curvature is correlated with galaxy morphology. The Einasto-like
shape of the outer stellar halo densities can also explain the observed
differences between the Milky Way and Andromeda outer stellar halos.
