The Case Against Warm or Self-Interacting Dark Matter as Explanations for Cores in Low Surface Brightness Galaxies

TL;DR

This study tests warm and self-interacting dark matter models against high-resolution galaxy rotation data, finding that these models cannot consistently explain the observed core sizes and densities in low surface brightness galaxies.

Contribution

The paper provides empirical constraints showing that WDM and SIDM models cannot account for the core properties in LSB galaxies, challenging their viability as explanations.

Findings

Core sizes increase with halo mass, contrary to WDM predictions.

Inferred core densities vary widely without systematic trend.

Primordial phase space densities required are inconsistent with Lyman alpha constraints.

Abstract

Warm dark matter (WDM) and self-interacting dark matter (SIDM) are often motivated by the inferred cores in the dark matter halos of low surface brightness (LSB) galaxies. We test thermal WDM, non-thermal WDM, and SIDM using high-resolution rotation curves of nine LSB galaxies. We fit these dark matter models to the data and determine the halo core radii and central densities. While the minimum core size in WDM models is predicted to decrease with halo mass, we find that the inferred core radii increase with halo mass and also cannot be explained with a single value of the primordial phase space density. Moreover, if the core size is set by WDM particle properties, then even the smallest cores we infer would require primordial phase space density values that are orders of magnitude smaller than lower limits obtained from the Lyman alpha forest power spectra. We also find that the dark matter halo core densities vary by a factor of about 30 from system to system while showing no systematic trend with the maximum rotation velocity of the galaxy. This strongly argues against the core size being directly set by large self-interactions (scattering or annihilation) of dark matter. We therefore conclude that the inferred cores do not provide motivation to prefer WDM or SIDM over other dark matter models.