Addressing the core-cusp and diversity problem of dwarf and disk galaxies using cold collisionless DARKexp theory

TL;DR

This paper demonstrates that the DARKexp statistical mechanics model can naturally produce flat density cores and diverse rotation curves in dwarf and disk galaxies, addressing longstanding core-cusp and diversity problems without baryonic feedback or alternative dark matter.

Contribution

It introduces the DARKexp model as a novel theoretical approach capable of fitting observed galaxy rotation curves and density profiles, solving key issues in galaxy formation theories.

Findings

DARKexp fits 96 SPARC galaxy rotation curves across 20-200 km/s.

DARKexp models ultrafaint dwarf stellar densities effectively.

Wave dark matter cannot fit the full range of observed galaxy profiles.

Abstract

Dwarf galaxies are observed to have linearly rising rotation curves, which indicate constant density cores in their centers. These do not arise naturally from dark matter only simulations, giving rise to the ``core-cusp'' problem. Hydrodynamic simulations incorporating baryonic feedback can create cored profiles, but this solution requires some fine tuning. Additionally, there is a related ``diversity'' problem in which simulations cannot reproduce the large range in rotation curve shapes for galaxies of similar mass. Here we investigate, for the first time, whether a theoretical model based on statistical mechanics (DARKexp) can produce flat density cores with its single shape parameter. We find that these theoretical profiles are able to fit the observed rotation curves of galaxies with last measured velocities in the range ~ 20-200 km/s by producing fits to 96 SPARC catalog galaxies covering this range. We additionally show that the projected stellar density distributions of ultrafaint dwarfs that show cores are also well fit, and that wave, or fuzzy dark matter is unable to fit the full range of SPARC galaxies. Thus, DARKexp appears to be able to address the core-cusp problem and the diversity of rotation curves in these dark matter dominated galaxies with cold collisionless dark matter alone, i.e., without introducing baryonic feedback, or alternative nature of dark matter.