Alignment between satellite and central galaxies in the SDSS DR7:
  dependence on large-scale environment
  The alignment between satellites and central galaxies has been studied in
detail both in observational and theoretical works. The widely accepted fact is
that the satellites preferentially reside along the major axis of their central
galaxy. However, the origin and large-scale environment dependence of this
alignment are still unknown. In an attempt to figure out those, we use data
constructed from SDSS DR7 to investigate the large-scale environmental
dependence of this alignment with emphasis on examining the alignments'
dependence on the colour of the central galaxy. We find a very strong
large-scale environmental dependence of the satellite-central alignment in
groups with blue centrals. Satellites of blue centrals in knots are
preferentially located perpendicular to the major axis of the centrals, and the
alignment angle decreases with environment namely when going from knots to
voids. The alignment angle strongly depend on the ${}^{0.1}(g-r)$ colour of
centrals. We suggest that the satellite-central alignment is the result of a
competition between satellite accretion within large scale-structure and galaxy
evolution inside host haloes. For groups containing red central galaxies, the
satellite-central alignment is mainly determined by the evolution effect, while
for blue central dominated groups, the effect of large-scale structure plays a
more important role, especially in knots. Our results provide an explanation
for how the satellite-central alignment forms within different large-scale
environments. The perpendicular case in groups and knots with blue centrals may
also provide insight into understanding similar polar arrangements such the
formation of the Milky Way and Centaurus A's satellite system.
