Galaxy pre-processing in substructures around z$\sim$0.4 galaxy clusters

TL;DR

This study investigates galaxy colour distributions in two z~0.4 galaxy clusters, revealing that pre-processing in substructures significantly influences galaxy quenching and passive galaxy formation.

Contribution

It provides the first detailed analysis of galaxy colours in substructures at z~0.4, highlighting the role of pre-processing in galaxy evolution within clusters.

Findings

Colour fractions in substructures follow the same spatial trends as main clusters.

Blue galaxy fraction at large distances is lower than in the field.

Pre-processing efficiency becomes comparable to cluster quenching at large radii.

Abstract

We present a detailed analysis of galaxy colours in two galaxy clusters at \mbox{z $\sim$ 0.4}, \mbox{MACS J0416.1-2403} and \mbox{MACS J1206.2-0847}, drawn from the CLASH-VLT survey, to investigate the role of pre-processing in the quenching of star formation. We estimate the fractions of red and blue galaxies within the main cluster and the detected substructures and study the trends of the colour fractions as a function of the projected distance from the cluster and substructure centres. Our results show that the colours of cluster and substructure members have consistent spatial distributions. In particular, the colour fractions of galaxies inside substructures follow the same spatial trends observed in the main clusters. Additionally, we find that at large cluster-centric distances \mbox{($r \geq r_{200}$)} the fraction of blue galaxies in both the main clusters and in the substructures is always lower than the average fraction of UVJ-selected star-forming galaxies in the field as measured in the COSMOS/UltraVista data set. We finally estimate environmental quenching efficiencies in the clusters and in the substructures and find that at large distances from the cluster centres, the quenching efficiency of substructures becomes comparable to the quenching efficiency of clusters. Our results suggest that pre-processing plays a significant role in the formation and evolution of passive galaxies in clusters at low redshifts.