# Predicted MOND velocity dispersions for a catalog of ultra-diffuse galaxies in group environments

## TL;DR

This paper predicts the velocity dispersions of 22 ultra-diffuse galaxies in group environments under MOND, considering the External Field Effect, to test the theory with future observations.

## Contribution

It provides the first a priori MOND velocity dispersion predictions for a sample of ultra-diffuse galaxies, including the effects of the External Field Effect.

## Key findings

- In 17 out of 22 cases, the External Field Effect significantly influences velocity dispersion predictions.
- The predictions account for variations in mass-to-light ratio and galaxy distance.
- The results set the stage for future observational tests of MOND in galaxy groups.

## Abstract

The possibility that ultra-diffuse galaxies lacking dark matter has recently stimulated interest to check the validity of Modified Newton Dynamics (MOND) predictions on the scale of such galaxies. It has been shown that the External Field Effect (EFE) induced by the close-by galaxy can suppress the velocity dispersion of these systems, so that they appear almost dark matter free in the Newtonian context. Here, following up on this, we are making a priori predictions for the velocity dispersion of 22 ultra-diffuse galaxies in the nearby Universe. This sample can be used to test MOND and the EFE with future follow-up measurements. We construct a catalog of nearby ultra-diffuse galaxies in galaxy group environments, and set upper and lower limits for the possible velocity dispersion allowed in MOND, taking into account possible variations in the mass-to-light ratio of the dwarf and in the distance to the galaxy group. The prediction for the velocity dispersion is made as a function of the three dimensional separation of the dwarf to its host. In 17 out of 22 cases, the EFE plays a crucial role in the prediction.