Dark matter haloes from dwarf to massive galaxies: No systematic inner-density tension with ΛCDM hydrodynamical simulations

Abstract

Two of the most prominent small-scale challenges to the standard cold dark matter (CDM) paradigm are the cusp--core and diversity-of-rotation-curves problems. The former concerns the shallow inner dark matter density profiles inferred for many galaxies compared with the cusps predicted by collisionless CDM simulations, while the latter concerns the wider range of inner dark matter densities and rotation curve shapes inferred observationally than hydrodynamical simulations traditionally reproduce. Robust observational constraints on dark matter core sizes and inner halo densities are therefore essential for testing both the nature of dark matter and the impact of galaxy formation processes. In this work, we analyse the inner dark matter distribution of a curated sample of 48 gas-rich disc galaxies and eight Milky Way gas-poor satellites, spanning six orders of magnitude in stellar mass (M_*). We find substantial galaxy-to-galaxy scatter in dark matter core sizes and degrees of coreness, with both cuspy and cored haloes occurring over a broad range in M_*. The inferred cores are energetically consistent with stellar feedback, requiring modest supernova energy coupling efficiencies typically of the order of 0.1 - 1%. Comparisons with the NIHAO, FIRE-2, and EDGE hydrodynamical simulations reveal broad agreement in the inner dark matter densities and logarithmic slopes of observed and simulated galaxies, both at homologous halo radii and at fixed physical scales. The main residual differences concern the steep slopes of some massive simulated galaxies (arguably due to baryonic contraction) and differences in the stellar-to-halo mass relation. Applying a diagnostic of rotation-curve diversity used in previous work, we find that the extreme discrepancies with simulations are absent from our curated sample and are largely attributable to uncertain kinematics or baryonic mass distributions. Within the observational and numerical scope of our analysis, we find no evidence of a systematic inner-density tension between our galaxy sample and current ΛCDM hydrodynamical simulations. Together with the modest energetic requirements for core formation, this substantially alleviates the cusp-core and diversity-of-rotation-curves problems.