Constraints on Dark Matter Halo Profiles from Dwarf Spheroidal Galaxy Kinematics

Abstract

Background

Dwarf spheroidal galaxies are the most dark-matter-dominated systems known, making them ideal laboratories for constraining the properties of dark matter halos. The inner density profile slope—whether cuspy (as predicted by NFW) or cored—remains a key discriminant between cold dark matter and alternative models.

Methods

We obtained multi-object spectroscopy of 450 individual red giant branch stars across six classical dwarf spheroidal satellites of the Milky Way using the VLT/FLAMES instrument. Line-of-sight velocity dispersions were measured with median uncertainties of 2.1 km/s. We fit spherically symmetric Jeans equation models with a generalized NFW profile to constrain the inner slope parameter γ.

Results

The median inner slope across our sample is γ = 0.41 ± 0.18, significantly shallower than the NFW prediction of γ = 1.0 (3.3σ tension). Sculptor and Fornax show the strongest evidence for cored profiles, while Draco and Ursa Minor are consistent with either cored or mildly cuspy distributions within current uncertainties.

Conclusions

Our results support a cored dark matter distribution in dwarf spheroidal galaxies. Baryonic feedback processes or warm dark matter models may be required to reconcile N-body simulations with the observed kinematic data. Upcoming spectroscopic surveys with 4MOST and WEAVE will provide the statistical power to definitively distinguish between competing dark matter models.