Lessons from the Local Group (and beyond) on dark matter
  (Abridged) The existence of exotic dark matter particles outside the standard
model of particle physics constitutes a central hypothesis of the current
standard model of cosmology (SMoC). Using a wide range of observational data I
outline why this hypothesis cannot be correct for the real Universe. Assuming
the SMoC to hold, (i) the two types of dwarf galaxies, the primordial dwarfs
with dark matter and the tidal dwarf galaxies without dark matter, ought to
present clear observational differences. But there is no observational evidence
for two separate families of dwarfs, neither in terms of their location
relative to the baryonic Tully-Fisher relation nor in terms of their
radius--mass relation. And, the arrangements in rotating disk-of-satellites, in
particular around the Milky Way and Andromeda, has been found to be only
consistent with most if not all dwarf satellite galaxies being tidal dwarf
galaxies. The highly symmetric structure of the entire Local Group too is
inconsistent with its galaxies stemming from a stochastic merger-driven
hierarchical buildup over cosmic time. (ii) Dynamical friction on the expansive
and massive dark matter halos is not evident in the data. Taking the various
lines of evidence together, the hypothesis that dynamically relevant exotic
dark matter exists needs to be firmly rejected.
