Understanding the "Feeble Giant" Crater II with tidally stretched Wave Dark Matter

Abstract

The unusually large, "feeble dwarf" galaxy Crater II, with its small velocity dispersion, 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 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, 𝜓DM, 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 𝜓DM prediction, with consistency found between its large core and low velocity dispersion for a boson mass of 𝑚 𝜓 𝑐 2 (1.9 ± 0.3) × 10 −22 eV. Similar core-halo structure is also apparent in most dwarf spheroidal galaxies (dSph), but with typically smaller cores, 0.25 kpc and higher velocity dispersions, 9km/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 𝜓DM, 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 20 kpc, now established by GAIA, implying significant tidal stripping by the Milky Way.

Not so fuzzy: excluding FDM with sizes and stellar kinematics of ultra-faint dwarf galaxies

“…Early work using FDM simulations found a tight scaling relation between the soliton mass and the virial mass of the host halo [8], leading to a number of papers attempting to constrain the FDM particle mass by finding evidence for either the presence or absence of massive solitons in nearby galaxies [9][10][11][12][13]. More recent FDM simulations covering larger cosmological volumes, however, discount the existence of a tight scaling relation between * ndalal@pitp.ca soliton mass and host halo mass, and instead indicate a large scatter in the correlation [14,15].…”