  Recent observations have revealed that high surface-brightness, metal-rich
debris is present over large regions of the Andromeda (M31) stellar halo. We
use a set of numerical models to determine whether extended metal-rich debris
is expected to exist in galaxy halos formed in a hierarchical LambdaCDM
universe. We identify tidal debris in the simulations according to the current
best surface brightness detection limits in M31 and demonstrate that bright
features in the outer halo regions usually originate from single satellites,
with very little contamination from other sources due to the low probability of
tidal streams from two overlapping accretion events. In contrast, high-surface
brightness features in the inner halo often originate from multiple
progenitors. We also compare the age and metallicity distribution of the debris
with the well-mixed stellar halos in which they reside. We find that
high-surface brightness tidal debris is produced almost exclusively by
relatively high mass progenitors (Mstar ~ 10^7- 10^9 Msun) and thus is expected
to be of moderate- to high-metallicity. Similarly, in our models the smooth
inner halo is expected to be metal-rich as this region has been built up mainly
from massive satellites. Our results imply that the stellar populations of
substructure observed around external galaxies with current techniques should
not resemble old and metal-poor dwarf spheroidal satellites, nor the underlying
component of the stellar halo.
