Origin of low-central-dark-matter regions

Determine the physical origin of the low-dark-matter-density regions observed in the central parts of nearby galaxies, whose radial extent increases with stellar mass and which are less dense than predicted by current cosmological simulations.

Background

The paper combines inner stellar kinematics with extended integrated neutral-hydrogen spectra to infer dark-matter density profiles for 136 nearby galaxies spanning stellar masses from approximately 109 to 1011.5 solar masses. It finds that galaxies above roughly 1010 solar masses have central dark-matter densities substantially below those predicted by several cosmological hydrodynamical simulations.

The discrepancy could reflect alternative dark-matter physics, feedback-driven expansion of the dark-matter distribution, differences in halo mass or concentration, or other missing ingredients in galaxy-formation simulations. The observations establish the existence of the low-density regions but do not identify their physical mechanism.

References

Baryonic processes such as AGN feedback and mergers may contribute to the inferred deficit, but whether they can reproduce its systematic growth across the observed mass range remains to be shown.

— Mass-Dependent Dark Matter Deficit from Inelastic Scattering  (2609.29114 - Yang et al., 24 Sep 2026) in Section “Discussion and conclusions,” paragraph beginning “Baryonic processes such as AGN feedback and mergers…”

We identify central regions with lower dark matter densities relative to $\Lambda$CDM simulation expectations—whose extent grows from about 10 kpc to $>50$ kpc as stellar mass increases from $10{10} M_{\odot}$ to $10{11.5} M_{\odot}$. Although their physical origin remains unclear, these low–dark matter regions are clearly indicated by the data.

— Lower central dark matter densities in nearby galaxies than predicted by simulations  (2609.16740 - Lei et al., 15 Sep 2026) in Abstract; Section 3, Discussion