The Impact of Cluster Mergers on Galaxy Properties

TL;DR

This study investigates how galaxy cluster mergers influence star formation in resident galaxies, finding only mild and statistically insignificant effects, and suggests galaxy mixing in merging clusters impacts star formation activity.

Contribution

It provides new insights into the effects of cluster mergers on galaxy star formation by analyzing multiple merging and relaxed clusters using spectroscopic data.

Findings

Mild, statistically insignificant increase in star-forming galaxy fraction in merging clusters

SFGs are well-mixed with passive galaxies in merging clusters

No strong evidence of triggered star formation related to dynamical state

Abstract

The impact of galaxy cluster mergers on the properties of the resident galaxies remains poorly understood. In this paper, we investigate the effects of merging environments on star formation (SF) activity in nearby clusters ($0.04<z<0.06$) from the SAMI Galaxy Survey - A168, A2399, A3380, and EDCC 0442 - which exhibit different dynamical activity. Using single-fibre spectroscopy from the SAMI Cluster Redshift Survey and Sloan Digital Sky Survey, we trace SF activity across the cluster sample by identifying the star-forming galaxy (SFG) population based on spectral features. We find a mild enhancement in the star-forming galaxy fraction ($f_{SFG}$) in merging clusters, although not statistically significant. The spatial and projected phase-space distributions show that SFGs in merging clusters are well-mixed with the passive population, while galaxy populations exhibit a clear segregation in the relaxed clusters. Analysis of the equivalent width of the $\rm H\alpha$ line, as a tracer of recent SF activity, does not reveal strong evidence of triggered SF activity as a function of dynamical state for both the global cluster environment and subsamples of galaxies selected near possible merger features. This suggests that the increase in $f_{SFG}$ is due to the mixing of galaxies in dynamically complex, young merging systems that are still forming, unlike their older, relaxed counterparts that have had longer to quench.