Dark-matter-deficient dwarf galaxies form via tidal stripping of dark
  matter in interactions with massive companions
  In the standard Lambda-CDM paradigm, dwarf galaxies are expected to be
dark-matter-rich, as baryonic feedback is thought to quickly drive gas out of
their shallow potential wells and quench star formation at early epochs. Recent
observations of local dwarfs with extremely low dark matter content appear to
contradict this picture, potentially bringing the validity of the standard
model into question. We use NewHorizon, a high-resolution cosmological
simulation, to demonstrate that sustained stripping of dark matter, in tidal
interactions between a massive galaxy and a dwarf satellite, naturally produces
dwarfs that are dark-matter-deficient, even though their initial dark matter
fractions are normal. The process of dark matter stripping is responsible for
the large scatter in the halo-to-stellar mass relation in the dwarf regime. The
degree of stripping is driven by the closeness of the orbit of the dwarf around
its massive companion and, in extreme cases, produces dwarfs with
halo-to-stellar mass ratios as low as unity, consistent with the findings of
recent observational studies. ~30 per cent of dwarfs show some deviation from
normal dark matter fractions due to dark matter stripping, with 10 per cent
showing high levels of dark matter deficiency (Mhalo/M*<10). Given their close
orbits, a significant fraction of dark-matter-deficient dwarfs merge with their
massive companions (e.g. ~70 per cent merge over timescales of ~3.5 Gyrs), with
the dark-matter-deficient population being constantly replenished by new
interactions between dwarfs and massive companions. The creation of these
galaxies is, therefore, a natural by-product of galaxy evolution and their
existence is not in tension with the standard paradigm.
