Galaxy rotation curves in modified gravity models

TL;DR

This study tests modified gravity models with a Yukawa potential to explain galaxy rotation curves, finding improved fits and constraints on the fifth-force parameters, suggesting a possible alternative to dark matter.

Contribution

It introduces a Yukawa term in gravity models and constrains its parameters using galaxy rotation data, showing improved fit over standard models.

Findings

Yukawa term improves fit quality significantly.

Best-fit Yukawa parameters are $eta=0.34$ and $\lambda=5.61$kpc.

Dark matter content reduces by 20% with Yukawa inclusion.

Abstract

In this work, we investigate the possibility that the galaxy rotation curves can be explained in the framework of modified gravity models that introduce a Yukawa term in the gravitational potential. We include dark matter and assume that the fifth-force couples differently to dark matter and to baryons. We aim at constraining the modified gravity parameters $\beta$ and $\lambda$, that is, the strength and the range of the Yukawa fifth force, respectively, using a set of 40 galaxy rotation curves data from the SPARC catalogue. We include baryonic gas, disk and bulge components, along with a NFW halo of dark matter. Each galaxy rotation curve is modeled with three free parameters, beside the two global Yukawa parameter. We find that the inclusion of the Yukawa term improves the $\chi^2$ from $680.75$ to $536.23$ for $655$ degrees of freedom. As global best-fit we obtain $\beta = 0.34\pm0.04$ and $\lambda = 5.61\pm0.91$kpc and a dark matter content on average 20\% smaller than without the Yukawa term. The Bayesian evidence in favor of a NFW profile plus Yukawa term is higher than 8$\sigma$ with respect to the standard gravity parametrization.