Galaxy collisions as a mechanism of ultra diffuse galaxy (UDG) formation

TL;DR

This paper proposes that galaxy collisions, especially in clusters like Coma, can strip gas from young, gas-rich galaxies, leading to the formation of ultra diffuse galaxies with low surface brightness and intact globular cluster systems.

Contribution

It introduces a novel collision-based mechanism for UDG formation and demonstrates its effectiveness in explaining observed properties in galaxy clusters.

Findings

The mechanism can produce UDGs with properties matching observations.

UDGs formed by this process are concentrated towards cluster centers.

Globular cluster systems of UDGs remain undamaged, consistent with observations.

Abstract

We suggest a possible mechanism of ultra diffuse galaxy formation: the UDGs may occur as a result of a central collision of galaxies. If the galaxies are young and contain a lot of gas, the collision may kick all the gas off the systems and thus strongly suppress any further star formation. As a result, the galaxies now have a very low surface brightness and other properties typical of the ultra diffuse galaxies. We use the Coma cluster (where numerous UDGs were recently discovered) to test the efficiency of the process. The mechanism works very well and can transform a significant fraction of the cluster population into ultra diffuse galaxies. The UDGs formed by the process concentrate towards the center of the cluster, and their globular cluster systems remain undamaged, in accordance with observational results. The projected surface density of UDGs in the cluster may help us to recognize the mechanism of UDG formation, or clarify relative contributions of several possible competitive mechanisms at work.