Newtonian limit of scalar-tensor theories and galactic dynamics: isolated and interacting galaxies

TL;DR

This paper investigates how scalar-tensor theories of gravity, with a Yukawa potential modification, influence galactic dynamics, particularly bar formation in isolated and interacting galaxies, revealing parameter-dependent destabilization effects.

Contribution

It introduces a numerical framework to study the impact of scalar-tensor gravity modifications on galaxy evolution, focusing on bar formation and interactions.

Findings

Positive alpha destabilizes galactic discs leading to rapid bar formation.

Optimal lambda range (8-14 kpc) produces the strongest bars.

Tidal interactions influence bar properties depending on scalar-tensor parameters.

Abstract

We use the Newtonian limit of a general scalar-tensor theory around a background field to study astrophysical effects. The gravitational theory modifies the standard Newtonian potential by adding a Yukawa term to it, which is quantified by two theoretical parameters: $\lambda$, the lenghtscale of the gravitational interaction and its strength, $\alpha$. Within this formalism we firstly present a numerical study on the formation of bars in isolated galaxies. We have found for positive $\alpha$ that the modified gravity destabilizes the galactic discs and leads to rapid bar formation in isolated galaxies. Values of $\lambda$ in the range $\approx 8$ -- 14 kpc produce strongest bars in isolated models. Then, we extent this work by considering tidal effects due to interacting galaxies. We send two spirals to collide and study the bar properties of the remnant. We characterize the bar kinematical properties in terms of our parameters ($\lambda, \alpha$).