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