Planes of satellites around simulated disc galaxies: I.- Finding
  high-quality planar configurations from positional information and their
  comparison to MW/M31 data
  We address the 'plane of satellites problem' by studying planar
configurations around two disc galaxies with no late major mergers, formed in
zoom-in hydro-simulations. Due to the current lack of good quality kinematic
data for M31 satellites, we use only positional information. So far, positional
analyses of simulations are unable to find planes as thin and populated as the
observed ones. Moreover, they miss systematicity and detail in the
plane-searching techniques, as well as in the study of the properties and
quality of planes, both in simulations or real data. To fill this gap, i) we
extend the 4-galaxy-normal density plot method (Pawlowski et al. 2013) in a way
designed to efficiently identify the best quality planes (i.e., thin and
populated) without imposing extra constraints on their properties, and ii), we
apply it for the first time to simulations. Using zoom-in simulations allows us
to mimic MW/M31-like systems regarding the number of satellites involved as
well as the galactic disc mass and morphology, in view of possible disc
effects. At all timesteps analyzed in both simulations we find satellite planar
configurations that are compatible, along given time intervals, with all the
spatial characteristics of observed planes identified using the same
methodology. However, the fraction of co-orbiting satellites within them is in
general low, suggesting time-varying satellite membership. We conclude that
high-quality positional planes of satellites are not infrequent in LCDM-formed
disc galaxies with a quiet assembly history. Detecting kinematically-coherent,
time-persistent planes demands considering the full six-dimensional phase-space
information of satellites.
