Reproducing the full abundance and phase-space distributions of Milky Way–type satellite systems in standard dark-matter models

Determine whether standard dark-matter-based cosmological models can reproduce the full abundance and phase-space distributions of satellite galaxies around Milky Way–type hosts, consistent with observed data.

Background

This paper applies Chandrasekhar dynamical friction constraints to multiple systems, including Milky Way dwarf spheroidal (dSph) satellites, arguing that capture within a massive Milky Way dark halo requires satellite halo masses exceeding those permitted by standard abundance matching and structure-formation expectations. The authors note that semi-analytical orbit integrations and analytical estimates disfavour capture solutions for several classical dSphs unless implausibly large pre-infall dark matter halos are assumed.

In this context, the paper emphasizes a broader unresolved issue: standard dark-matter-based cosmological models have difficulty simultaneously matching the observed abundance (numbers) and phase-space (positions and velocities) distributions of satellites around Milky Way–type hosts. This is flagged as a persisting unsolved challenge even allowing for uncertainties such as tidal stripping and evolving host halos.

References

It remains true that full abundance and phase space distributions of satellites of MW-type galaxies remain a very major unsolved challenge within the standard dark matter scenarios.

— Dynamical Friction Constraints on the Dark Matter Hypothesis Across Astronomical Scales  (2511.03776 - Hernandez et al., 5 Nov 2025) in Section 7.1 (The dSph Satellite Galaxies of the MW)

While astrophysical baryonic processes may alleviate some of these tensions, their ultimate origin remains an open question.

— Testing MOND-like modifications to gravity using growth-rate measurements and one-loop corrections to the matter power spectrum  (2608.18229 - Hartmann et al., 18 Aug 2026) in Section 1, Introduction