Thermalization, Fragmentation and Tidal Disruption: The Complex Galactic Dynamics of Dark Matter Superfluidity

TL;DR

This paper explores the behavior of self-interacting bosonic dark matter that can form a superfluid, leading to unique halo structures, fragmentation into clumps, and implications for galaxy rotation curves, especially in dwarf galaxies.

Contribution

It demonstrates that superfluid dark matter halos undergo Bose-Einstein condensation, fragment into clumps, and explains the diversity of dwarf galaxy rotation curves within this framework.

Findings

Dark matter halos fully thermalize and condense into superfluids.

Halo fragmentation results in superfluid clumps that are tidally disrupted.

Central solitons can be large and influence galaxy rotation curves.

Abstract

The idea of self-interacting bosonic dark matter capable of exhibiting superfluidity is revisited. We show that the most interesting parameter space of the theory corresponds to fully thermalized dark matter halos. As a result the entire halo undergoes Bose-Einstein condensation due to high degeneracy. Since it is observationally preferable for the dark matter density profile to be similar to cold dark matter in the outskirts of the halo, we argue that the Jeans wavelength must be at least few times shorter than the virial radius. This entails that, upon condensation, a dark matter halo fragments into superfluid clumps. However, we demonstrate that these would-be solitons experience strong tidal disruption and behave as virialized weakly interacting streams. An exception is the central soliton, which can be as large as few tens of kiloparsecs in size without contradicting observational bounds. As a result, in dwarf galaxies, the observed rotation curves can be completely contained within the superfluid soliton. In this case, the dark matter distribution is expected to be strongly sensitive to the baryonic density profile. We argue that the diversity of rotation curves observed for dwarf galaxies is a natural consequence of the superfluid dark matter scenario.