Caught in the rhythm: how satellites settle into a plane around their
  central galaxy
  Using the cosmological hydrodynamics simulation Horizon-AGN, we investigate
the spatial distribution of satellite galaxies relative to their central
counterpart in the redshift range between 0.3 and 0.8. We find that, on
average, these satellites tend to be located on the galactic plane of the
central object. This effect is detected for central galaxies with a stellar
mass larger than 10^10 solar masses and found to be strongest for red passive
galaxies, while blue galaxies exhibit a weaker trend. For galaxies with a minor
axis parallel to the direction of the nearest filament, we find that the
coplanarity is stronger in the vicinity of the central galaxy, and decreases
when moving towards the outskirts of the host halo. By contrast, the spatial
distribution of satellite galaxies relative to their closest filament follows
the opposite trend: their tendency to align with them dominates at large
distances from the central galaxy, and fades away in its vicinity. Relying on
mock catalogs of galaxies in that redshift range, we show that massive red
centrals with a spin perpendicular to their filament also have corotating
satellites well aligned with both the galactic plane and the filament. On the
other hand, lower-mass blue centrals with a spin parallel to their filament
have satellites flowing straight along this filament, and hence orthogonally to
their galactic plane. The orbit of these satellites is then progressively bent
towards a better alignment with the galactic plane as they penetrate the
central region of their host halo. The kinematics previously described are
consistent with satellite infall and spin build-up via quasi-polar flows,
followed by a re-orientation of the spin of massive red galaxies through
mergers.
