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

TL;DR

This paper explains the unusual properties of the dwarf galaxy Crater II using wave dark matter theory, suggesting it was a typical dwarf galaxy that lost mass through tidal interactions with the Milky Way.

Contribution

It demonstrates that Crater II's core-halo structure aligns with wave dark matter predictions and proposes a tidal stripping scenario to explain its low velocity dispersion.

Findings

Crater II has a prominent dark matter core of about 0.71 kpc.

The core-halo profile matches wave dark matter (ψDM) predictions.

Crater II likely experienced significant tidal stripping by the Milky Way.

Abstract

The unusually large "dwarf" galaxy Crater II, with its small velocity dispersion, $\simeq 3$ km/s, defies expectations that low mass galaxies should be small and dense. We combine the latest stellar and velocity dispersion profiles finding Crater II has a prominent dark core of radius $\simeq 0.71^{+0.09}_{-0.08}$ kpc, surrounded by a low density halo, with a transition visible between the core and the halo. We show that this profile matches the distinctive core-halo profile predicted by "Wave Dark Matter" as a Bose-Einstein condensate, $\psi$DM, where the ground state soliton core is surrounded by a tenuous halo of interfering waves, with a marked density transition predicted between the core and halo. Similar core-halo structure is seen in most dwarf spheroidal galaxies (dSph), but with smaller cores, $\simeq 0.25$ kpc and higher velocity dispersions, $\simeq 9$km/s, and we argue here that Crater II may have been a typical dSph that has lost most of its halo mass to tidal stripping, so its velocity dispersion is lower by a factor of 3 and the soliton is wider by a factor of 3, following the inverse scaling required by the Uncertainty Principle. This tidal solution for Crater II in the context of $\psi$DM, is supported by its small pericenter of $\simeq 20$ kpc established by Gaia, implying significant tidal stripping of Crater II by the Milky Way is expected.