Clash of Titans: The Impact of Cluster Mergers in the Galaxy Cluster Red Sequence

TL;DR

This study investigates how galaxy cluster mergers influence galaxy populations by analyzing color-magnitude diagrams across different redshifts, revealing that merger effects vary with cosmic time and cluster dynamical state.

Contribution

It provides new insights into the impact of cluster mergers on galaxy evolution, highlighting differences in galaxy color distributions at various redshifts and dynamical states.

Findings

High-z clusters are richer in blue galaxies regardless of dynamical state.

Disturbed high-z clusters show more scatter and bluer galaxies in the Red Sequence.

At low-z, relaxed and disturbed clusters show similar galaxy populations.

Abstract

Merging of galaxy clusters are some of the most energetic events in the Universe, and they provide a unique environment to study galaxy evolution. We use a sample of 84 merging and relaxed SPT galaxy clusters candidates, observed with the Dark Energy Camera in the $0.11<z<0.88$ redshift range, to build colour-magnitude diagrams to characterize the impact of cluster mergers on the galaxy population. We divided the sample between relaxed and disturbed, and in two redshifts bin at $z = 0.55$. When comparing the high-z to low-z clusters we find the high-z sample is richer in blue galaxies, independently of the cluster dynamical state. In the high-z bin we find that disturbed clusters exhibit a larger scatter in the Red Sequence, with wider distribution and an excess of bluer galaxies compared to relaxed clusters, while in the low-z bin we find a complete agreement between the relaxed and disturbed clusters. Our results support the scenario in which massive cluster halos at $z<0.55$ galaxies are quenched as satellites of another structure, i.e. outside the cluster, while at $z \geq 0.55$ the quenching is dominated by in-situ processes.