# On the evolution of galaxy spin in a cosmological hydrodynamic simulation of galaxy clusters

## TL;DR

This study uses cosmological hydrodynamic simulations to explore how galaxy spins evolve in cluster environments, revealing that environmental effects and mergers influence spin down, with minor mergers having notable impact.

## Contribution

First simulation-based analysis of galaxy spin evolution in clusters, highlighting environmental effects and the roles of major and minor mergers.

## Key findings

- Galaxies spin down over cosmic time.
- Minor mergers have stronger cumulative effects than major mergers.
- Environmental effects are the dominant driver of spin down.

## Abstract

The traditional view of the morphology-spin connection is being challenged by recent integral-field-unit observations, as the majority of early-type galaxies are found to have a rotational component that is often as large as a dispersion component. Mergers are often suspected to be critical in galaxy spin evolution, yet the details of their roles are still unclear. We present the first results on the spin evolution of galaxies in cluster environments through a cosmological hydrodynamic simulation. Galaxies spin down globally with cosmic evolution. Major (mass ratios > 1/4) and minor (1/4 $\geq$ mass ratios > 1/50) mergers are important contributors to the spin down in particular in massive galaxies. Minor mergers appear to have stronger cumulative effects than major mergers. Surprisingly, the dominant driver of galaxy spin down seems to be environmental effects rather than mergers. However, since multiple processes act in combination, it is difficult to separate their individual roles. We briefly discuss the caveats and future studies that are called for.