Title: Can we tell the planes'' truth? On the suggested origins of co-orbiting planes of satellite 
galaxies

Abstract:
Both major galaxies in the Local Group (LG) host planar distributions of co-orbiting satellite 
galaxies: the Vast Polar Structure (VPOS) of the Milky Way and the Great Plane of Andromeda 
(GPoA). Similar structures, often associated with streams, are present around more distant hosts 
and might even be ubiquitous in the universe. I will discuss suggested formation scenarios for the 
satellite planes and their shortcomings. Even though not predicted by the ΛCDM model of 
cosmology, several recent studies claim that the VPOS and GPoA are consistent with sub-halo 
based satellites. Unfortunately, these studies either have flaws in their model satellite selection, 
do not consider all observational constraints, or are internally inconsistent. Correcting the 
analyses changes their results dramatically: the observed satellite galaxy planes remain extremely 
rare in ΛCDM simulations. Motivated by the fact that both major galaxies in the LG host mutually 
aligned satellite planes, I suggest that the LG can provide additional clues. Being part of a LG 
analog does not increase the chances of host halos in ΛCDM simulations to contain a VPOS-like 
satellite planes. However, I find that the observed phase-space distribution of the non-satellite 
dwarfs in the LG is also highly structured and indicates additional tensions with cosmological 
expectations, in particular in the number of likely backsplash galaxies and their distribution.