On the Spin Bias of Satellite Galaxies in the Local Group-like
  Environment
  We utilize the Millennium-II simulation databases to study the spin bias of
dark subhalos in the Local Group-like systems which have two prominent
satellites with comparable masses. Selecting the group-size halos with total
mass similar to that of the Local Group (LG) from the friends-of-friends halo
catalog and locating their subhalos from the substructure catalog, we determine
the most massive (main) and second to the most massive (submain) ones among the
subhalos hosted by each selected halo. When the dimensionless spin parameter
(lambda) of each subhalo is derived from its specific angular momentum and
circular velocity at virial radius, a signal of correlation is detected between
the spin parameters of the subhalos and the main-to-submain mass ratios of
their host halos at z=0: The higher main-to-submain mass ratio a host halo has,
the higher mean spin parameter its subhalos have. It is also found that the
correlations exist even for the subhalo progenitors at z=0.5 and z=1. Our
interpretation of this result is that the subhalo spin bias is not a transient
effect but an intrinsic property of a LG-like system with higher main-to-
submain mass ratio, caused by stronger anisotropic stress in the region. A
cosmological implication of our result is also discussed.
