Exploring velocity dispersion anisotropy in a dark matter dominated ultra-diffuse galaxy with modified gravity models

TL;DR

This study compares modified gravity models to dark matter in explaining the velocity dispersion of the ultra-diffuse galaxy NGC1052-DF44, finding that MOND and RGGR models fit observations well.

Contribution

It evaluates three alternative gravity models against dark matter in explaining galaxy kinematics, considering anisotropy effects, which is a novel comparative analysis.

Findings

All models fit the observed velocity dispersion.

MOND and RGGR are competitive with dark matter models.

Anisotropy assumptions influence model fits.

Abstract

The kinematics of the ultra-diffuse galaxy (UDG) NGC1052-DF44 is primarily influenced by the presence of dark matter (DM). In this paper, we conduct a contrasting kinematic study of DF44 within the alternative modified gravity framework. In comparison to NFW DM, we test three alternative gravity models viz Milgromian dynamics (MOND), characterized by a known acceleration scale, a generic $f(R)$ model, assuming an expansion of the Ricci scalar, and a quantum gravity-inspired Renormalization Group correction to General Relativity (RGGR), which involves the running of the gravitational coupling parameter $G$ with the Universe's energy scale. For each gravity model, we evaluate the velocity dispersion (VD) of the galaxy beyond the conventional radial isotropic assumption and extend to two anisotropy scenarios, i.e., constant and Osipkov-Merritt. Our results show that all three gravity models can provide consistent fits to the observed VD of DF44; however, only MOND and RGGR remain competitive with NFW DM. Interestingly, the constant anisotropy scenario in all the models is also found to be competitive with the complete isotropic assumption.