Galaxy Clusters in the Context of Superfluid Dark Matter

TL;DR

This paper develops spherical models of galaxy clusters within superfluid dark matter theory, demonstrating it can reproduce observed mass profiles but with some under-predictions in central regions, indicating further refinement is needed.

Contribution

First spherical models of galaxy clusters in superfluid dark matter are presented, linking superfluid core and normal phase halo to observed cluster mass profiles.

Findings

Superfluid dark matter can fit galaxy cluster mass profiles.

The model under-predicts gravity in cluster centers.

Neglecting phonons may affect the accuracy of the model.

Abstract

It has recently been proposed, by assuming that dark matter is a superfluid, that MOND-like effects can be achieved on small scales whilst preserving the success of $\Lambda$CDM on large scales. Here we aim to provide the first set of spherical models of galaxy clusters in the context of superfluid dark matter. We first outline the theoretical structure of the superfluid core and the surrounding "normal phase" dark halo of quasi-particles in thermal equlibrium. The latter should encompass the largest part of galaxy clusters. Here, we set the SfDM transition at the radius where the density and pressure of the superfluid and normal phase coincides, neglecting the effect of phonons in the suprefluid core. We then apply the theory to a sample of galaxy clusters, and directly compare the SfDM predicted mass profiles to data. We find that the superfluid formulation can reproduce the X-ray dynamical mass profile of clusters. The SfDM fits however display slight under-predictions of the gravity in the central regions which might be partly related to our neglecting of the effect of phonons in these regions. We conclude that this superfluid formulation is successful in describing galaxy clusters, but further work will be needed to determine whether the parameter choice is consistent with galaxies. Our model could be made more realistic by exploring non-sphericity and the SfDM transition condition we impose.