The Origin of Lopsided Satellite Galaxy Distribution in Galaxy Pairs
  It is well known that satellite galaxies are not isotropically distributed
among their host galaxies as suggested by most interpretations of the
$\Lambda$CDM model. One type of anisotropy recently detected in the SDSS (and
seen when examining the distribution of satellites in the Local Group and in
the Centaurus group) is a tendency to be so-called "lopsided". Namely, in pairs
of galaxies (like Andromeda and the Milky Way) the satellites are more likely
to inhabit the region in between the pair, rather than on opposing sides.
Although recent studies found a similar set up when comparing pairs of galaxies
in $\Lambda$CDM simulations indicating that such a set up is not inconsistent
with $\Lambda$CDM, the origin has yet to be explained. Here we examine the
origin of such lopsided setups by first identifying such distributions in pairs
of galaxies in numerical cosmological simulations, and then tracking back the
orbital trajectories of satellites (which at $z=0$ display the effect). We
report two main results: first, the lopsided distribution was stronger in the
past and weakens towards $z=0$. Second, the weakening of the signal is due to
the interaction of satellite galaxies with the pair. Finally, we show that the
$z=0$ signal is driven primarily by satellites that are on first approach, who
have yet to experience a "flyby". This suggests that the signal seen in the
observations is also dominated by dynamically young accretion events.
