The anisotropic distribution of satellites around the central galaxy of their
host halo is well-documented. However the relative impact of baryons and dark
matter in shaping this distribution is still debated. Using the simulation
Horizon-AGN, the angular distribution of satellite galaxies with respect to
their central counterpart and halo is quantified. Below one Rvir, satellites
cluster more strongly in the plane of the central, rather than merely tracing
the shape of their host halo. This is due to the increased isotropy of inner
haloes acquired through their inside-out assembly in vorticity-rich flows along
the cosmic web. While the effect of centrals decreases with distance, halos'
triaxiality increases, impacting more and more the satellite's distribution.
Effects become comparable just outside one virial radius. Above this scale, the
filamentary infall also impacts the satellites distribution, dominating above
two virial radii. The central's morphology plays a governing role: the
alignment w.r.t. the central plane is four times stronger in haloes hosting
stellar discs than in spheroids. But the impact of the galactic plane decreases
for lower satellite-to-central mass ratios, suggesting this might not hold for
dwarf satellites of the Local group. The orientation of the Milky-Way's
satellites traces their cosmic filament, their level of coplanarity is
consistent with systems of similar mass and cosmic location in Horizon-AGN.
However, the strong impact of galactic planes in massive groups and clusters
bounds the likelihood of finding a relaxed region where satellites can be used
to infer halo shape. The minor-to-major axis ratios for haloes with
log(M0/Msun)>13.5 is underestimated by 10%. This error soars quickly to 30-40%
for individual halo measurements.Comment: 30 pages, 28 figures, submitted to A&
