Unveiling the dynamical state of massive clusters through the ICL
  fraction
  We have selected a sample of eleven massive clusters of galaxies observed by
the Hubble Space Telescope in order to study the impact of the dynamical state
on the IntraCluster Light (ICL) fraction, the ratio of total integrated ICL to
the total galaxy member light. With the exception of the Bullet cluster, the
sample is drawn from the Cluster Lensing and Supernova Survey and the Frontier
Fields program, containing five relaxed and six merging clusters. The ICL
fraction is calculated in three optical filters using the CHEFs IntraCluster
Light Estimator, a robust and accurate algorithm free of a priori assumptions.
We find that the ICL fraction in the three bands is, on average, higher for the
merging clusters, ranging between $\sim7-23\%$, compared with the $\sim 2-11\%$
found for the relaxed systems. We observe a nearly constant value (within the
error bars) in the ICL fraction of the regular clusters at the three
wavelengths considered, which would indicate that the colors of the ICL and the
cluster galaxies are, on average, coincident and, thus, their stellar
populations. However, we find a higher ICL fraction in the F606W filter for the
merging clusters, consistent with an excess of lower-metallicity/younger stars
in the ICL, which could have migrated violently from the outskirts of the
infalling galaxies during the merger event.
