How does dark matter stabilize disc galaxies?

TL;DR

This paper develops a theoretical framework to analyze how dark matter halos influence the stability of galactic discs, showing that dark matter generally stabilizes galaxies but some early universe baryon-dominated discs remain unstable.

Contribution

It introduces a new stability criterion linking dark matter potential and gas fraction, and applies it to various galaxy models to assess dark matter's stabilizing role.

Findings

Dark matter halos increase galaxy stability against gravitational instabilities.

Baryon-dominated early universe galaxies remain unstable despite dark matter influence.

Dark matter's stabilizing effect varies with galaxy type and gas content.

Abstract

The study presents a theoretical framework for understanding the role of dark matter on the stability of the galactic disc. We model the galaxy as a two-component system consisting of stars and gas in equilibrium with an external dark matter halo. We derive the equations governing the growth of perturbations and obtain a stability criterion that connects the potential of the dark matter halo and the gas fraction with the stability levels of the galaxy. We find that a two-component disc is more susceptible to the growth of gravitational instabilities than individual components, particularly as gas fractions increase. However, the external field, due to the dark matter halo, acts as a stabilizing agent and increases the net stability levels even in the presence of a cold gas component. We apply the stability criterion to models of the Milky Way, low surface brightness galaxies, and baryon-dominated cold rotating disc galaxies observed in the early universe. Our results show that the potential due to the dark matter halo plays a significant role in stabilizing nearby galaxies, such as the Milky Way, and low surface brightness galaxies, which would otherwise be prone to local gravitational instabilities. However, we find that the baryon-dominated cold disc galaxies observed in the early universe remain susceptible to the growth of local gravitational instabilities despite the stabilizing effect of the dark matter halo.