Perseus I and the NGC 3109 association in the context of the Local Group
  dwarf galaxy structures
  The recently discovered dwarf galaxy Perseus I appears to be associated with
the dominant plane of non-satellite galaxies in the Local Group (LG). We
predict its velocity dispersion and those of the other isolated dSphs Cetus and
Tucana to be 6.5, 8.2, and 5.5 km/s, respectively. The NGC 3109 association,
including the recently discovered dwarf galaxy Leo P, aligns with the dwarf
galaxy structures in the LG such that all known nearby non-satellite galaxies
in the northern Galactic hemisphere lie in a common thin plane (rms height 53
kpc; diameter 1.2 Mpc). This plane has an orientation similar to the preferred
orbital plane of the Milky Way (MW) satellites in the vast polar structure.
Five of seven of these northern galaxies were identified as possible backsplash
objects, even though only about one is expected from cosmological simulations.
This may pose a problem, or instead the search for local backsplash galaxies
might be identifying ancient tidal dwarf galaxies expelled in a past major
galaxy encounter. The NGC 3109 association supports the notion that material
preferentially falls towards the MW from the Galactic south and recedes towards
the north, as if the MW were moving through a stream of dwarf galaxies.
