Dwarf Galaxy Constraints on Interacting Fermionic Dark Matter

TL;DR

This study uses dwarf galaxy stellar kinematic data to constrain fermionic dark matter models, finding that current observations favor fermion masses between 100 and 300 eV and do not strongly distinguish between interacting and non-interacting scenarios.

Contribution

It provides the first detailed comparison of interacting versus non-interacting degenerate fermionic dark matter models using dwarf galaxy data.

Findings

Fermion masses are constrained to 100-300 eV range.

Interacting and non-interacting models yield similar posterior distributions.

Current data do not favor significant interactions in fermionic dark matter.

Abstract

Dwarf galaxies in the Local Group offer a way to test dark matter (DM) models against stellar kinematic data. In this work, we study degenerate fermionic DM in two cases: the standard non-interacting Fermi gas, and an interacting degenerate DM fluid described by a phenomenological equation of state motivated by interacting Fermi systems. These interactions modify the compressibility of the DM fluid and, in some regions of parameter space, lead to mechanically unstable branches that must be treated through a Maxwell construction. We solve the corresponding non-relativistic hydrostatic equations consistently and compute the line-of-sight velocity-dispersion profiles using the spherical Jeans equation. We then perform MCMC fits to eight classical Milky Way dwarf spheroidal galaxies. The data favor DM fermion masses in the range $100$--$300\,{\rm eV}$. We find that the interacting and non-interacting equations of state give broadly similar posterior distributions for the fermion mass, central density, and stellar anisotropy. Current data therefore do not strongly prefer an interacting equation of state over the free degenerate Fermi-gas, thereby excluding large deviations from the non-interacting limit.