Understanding the "Feeble Giant" Crater II with tidally stretched Wave
  Dark Matter
  The unusually large, "feeble dwarf" galaxy Crater II, with its small velocity
dispersion, $\simeq 3$ km/s, defies expectations that low mass galaxies should
be small and dense. Here we examine its unusual properties in the context of
"Wave Dark Matter", combining the latest stellar and velocity dispersion
profiles for Crater II, finding a prominent dark core of radius $\simeq
0.71^{+0.09}_{-0.08}$ kpc, surrounded by a low density halo, with a visible
transition between the core and the halo. This observed behaviour is very
similar to the distinctive core-halo profile structure of dark matter as a
Bose-Einstein condensate, $\psi$DM, where the ground state forms a prominent
soliton core, surrounded by a tenuous halo of interfering waves, with a marked
density transition predicted between the soliton and the halo. Crater II
conforms well this distinctive $\psi$DM prediction, with consistency found
between its large core and low velocity dispersion for a boson mass of $m_\psi
c^2\simeq (1.9 \pm 0.3) \times10^{-22}$ eV. Similar core-halo structure is also
apparent in most dwarf spheroidal galaxies (dSph), but with typically smaller
cores, $\simeq 0.25$ kpc and higher velocity dispersions, $\simeq 9$km/s. We
argue that Crater II may have have been a more typical dSph dwarf that has lost
most of its halo mass to tidal stripping in the context of $\psi$DM, resulting
in a factor 3 reduction in velocity dispersion causing a threefold expansion of
the soliton core, following the inverse scaling between velocity and de Broglie
wavelength required by the Uncertainty Principle. This tidal origin for Crater
II is supported by its small pericenter of $\simeq 20$ kpc, now established by
GAIA, implying significant tidal stripping by the Milky Way.
