  Large-scale faint structure detected by the recent observations in the halo
of the Andromeda galaxy (M31) provides an attractive window to explore the
structure of outer cold dark matter (CDM) halo in M31. Using an N-body
simulation of the interaction between an accreting satellite galaxy and M31, we
investigate the mass density profile of the CDM halo. We find the sufficient
condition of the outer density profile of CDM halo in M31 to reproduce the
Andromeda giant stream and the shells at the east and west sides of M31. The
result indicates that the density profile of the outer dark matter halo of M31
is a steeper than the prediction of the theory of the structure formation based
on the CDM model.
