Evidence for a redshifted excess in the intracluster light fractions of merging clusters at $z\sim 0.8$

The intracluster light (ICL) fraction is a well-known indicator of the dynamical activity in intermediate-redshift clusters. Merging clusters in the redshift interval $0.18<z<0.56$ have a distinctive peak in the ICL fractions measured between $\sim 3800-4800$ \AA. In this work, we analyze two higher-redshift, clearly merging clusters, ACT-CLJ0102-49151 and CL J0152.7-1357, at $z>0.8$, using the HST optical and infrared images obtained by the RELICS survey. We report the presence of a similar peak in the ICL fractions, although wider and redshifted to the wavelength interval $\sim 5200-7300$ \AA. The fact that this excess in the ICL fractions is found at longer wavelengths can be explained by an assorted mixture of stellar populations in the ICL, direct inheritance of an ICL that was mainly formed by major galaxy mergers with the BCG at $z>1$ and whose production is instantaneously burst by the merging event. The ubiquity of the ICL fraction merging signature across cosmic time enhances the ICL as a highly reliable and powerful probe to determine the dynamical stage of galaxy clusters, which is crucial for cluster-based cosmological inferences that require relaxation of the sample.
Comment: 11 pages, 3 figures, accepted for publication in ApJL