Dark Matter Cores and Cusps in Spiral Galaxies and their Explanations

TL;DR

This paper compares dark matter models in spiral galaxies, showing self-interacting dark matter (SIDM) better explains observed core-cusp phenomena and their correlation with stellar brightness, compared to cold dark matter (CDM) simulations.

Contribution

It demonstrates that SIDM models, which include baryonic effects, better match galaxy rotation curves and core sizes than traditional CDM models, highlighting the need to revise feedback mechanisms.

Findings

SIDM predicts a strong core size and stellar surface density correlation.

SIDM provides the best fit to the SPARC galaxy rotation data.

CDM with strong feedback struggles to reproduce observed galaxy cores.

Abstract

We compare proposed solutions to the core vs cusp issue of spiral galaxies, which has also been framed as a diversity problem, and demonstrate that the cuspiness of dark matter halos is correlated with the stellar surface brightness. We compare the rotation curve fits to the SPARC sample from a self-interacting dark matter (SIDM) model, which self-consistently includes the impact of baryons on the halo profile, and hydrodynamical N-body simulations with cold dark matter (CDM). The SIDM model predicts a strong correlation between the core size and the stellar surface density, and it provides the best global fit to the data. The CDM simulations without strong baryonic feedback effects fail to explain the large dark matter cores seen in low surface brightness galaxies. On the other hand, with strong feedback, CDM simulations do not produce galaxy analogs with high stellar and dark matter densities, and therefore they have trouble in explaining the rotation curves of high surface brightness galaxies. This implies that current feedback implementations need to be modified. We also explicitly show how the concentration-mass and stellar-to-halo mass relations together lead to a radial acceleration relation (RAR) in an averaged sense, and reiterate the point that the RAR does not capture the diversity of galaxy rotation curves in the inner regions. These results make a strong case for SIDM as the explanation for the cores and cusps of field galaxies.