Considerations on how to investigate planes of satellite galaxies
  The existence of a spatially thin, kinematically coherent Disk of Satellites
(DoS) around the Milky Way (MW), is a problem that often garners vivacious
debate in the literature or at scientific meetings. One of the most recent
incarnations of this wrangle occurred with two papers by Maji et al, who argued
that these structures "maybe a misinterpretation of the data". These claims are
in stark contrast to previous works. Motivated by this and other recent
publications on this problem, we discuss necessary considerations to make,
observational effects to consider, and pitfalls to avoid when investigating
satellite galaxy planes such as the MW's DoS. In particular, we emphasize that
conclusions need to have a statistical basis including a determination of the
significance of satellite alignments, observational biases must not be ignored,
and measurement errors (e.g. for proper motions) need to be considered. We
discuss general problems faced by attempts to determine the dynamical stability
of the DoS via orbit integrations of MW satellite galaxies, and demonstrate
that to interpret simulations, it is helpful to compare them with a null case
of isotropically distributed satellite positions and velocities. Based on these
criteria, we find that the conclusions of Maji et al. do not hold up to
scrutiny, and that their hydrodynamic cosmological simulation of a single host
shows no evidence for a significant kinematic coherence among the simulated
satellite galaxies, in contrast to the observed MW system.
