Consequences of the external field effect for MOND disk galaxies in galaxy clusters

TL;DR

This study investigates how the external field effect in MOND influences the dynamics and morphology of disk galaxies in clusters, revealing increased asymmetries, mass loss, and altered rotation curves, especially in low-mass galaxies.

Contribution

It provides the first detailed analysis of the external field effect on galaxy dynamics within clusters in the context of MOND, considering various orbital configurations.

Findings

MOND cluster galaxies show isophote asymmetries.

Galaxies experience increased mass loss due to combined effects.

Low-mass galaxies become dispersion-dominated, losing rotational support.

Abstract

Galaxies within galaxy clusters are known to be subject to a wide variety of environmental effects, both gravitational and hydrodynamical. In this study, we examine the purely gravitational interaction of idealised galaxy models falling into a galaxy cluster in the context of Modified Newtonian Dynamics (MOND). This modification of gravity gives rise to an external field effect (EFE), where the internal dynamics of a system are affected by the presence of external gravitational fields. We examine the consequences of the EFE on low and high mass disk galaxies in time-evolving analytic background cluster potentials, considering orbits with weak and strong tidal fields. By varying the orbital plane of the galaxies we also test the effect of having the tidal interaction orthogonal or parallel to the disk. Furthermore, we consider as a control sample models where the EFE has been removed and they are only affected by tides. Our results suggest that MOND cluster galaxies should exhibit clear asymmetries in their isophotes, suffer increased mass loss and a reduction in their rotation curves due to the combined effect of cluster tides and the external field. In particular, low mass galaxies are hit hard by the EFE, becoming dominated by dispersion rather than rotation even in the absence of tides.