Discriminating merging from relaxed clusters using the intracluster light

The assessment of the relaxation level of galaxy clusters holds significant importance for their use as cosmological probes, particularly in the context of high-redshift clusters, where their cosmological utility is more discriminatory, despite the challenges posed by a heightened merger rate epoch. Conventional high-resolution X-ray observations of these high-z systems often lack the depth necessary for spatially resolved spectroscopy, impeding the accurate quantification of ICM inhomogeneities. A recent innovative approach to estimate the dynamical stage of clusters, using only optical (and/or NIR for high-z systems) information, has been gaining ground, specifically, looking at the distribution of intracluster light fractions at various wavelengths. This methodology has proven remarkably successful in distinguishing between merger and relaxed clusters, confirmed through X-rays, and we show some outstanding examples here. The efficacy of this approach suggests its potential incorporation into upcoming multi-filter large-scale surveys, such as J-PAS.