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  • Dissecting the RELICS clust...
    Jiménez-Teja, Y.; Dupke, R. A.; Lopes, P. A. A.; Vílchez, J. M.

    Astronomy & astrophysics, 08/2023, Volume: 676
    Journal Article

    The intracluster light (ICL) fraction, measured at certain specific wavelengths, has been shown to provide a good marker for determining the dynamical stage of galaxy clusters, that is, merging versus relaxed, for low to intermediate redshifts. We apply it for the first time to a high-redshift system, SPT-CLJ0615–5746 at z  = 0.97, using its Reionization Lensing Cluster Survey (RELICS) observations in the optical and infrared. We find the ICL fraction signature of the merging, with values ranging from 16 to 37%. A careful reanalysis of the X-ray data available for this cluster indicates at least one current and plausibly a second merger. These two results contradict previous works based on X-ray data, which claimed a relaxed state for SPT-CLJ0615–5746, and the results confirm the evidence presented by kinematic analyses. We also found an abnormally high ICL fraction in the rest-frame near-ultraviolet wavelengths, which may be attributed to the combination of several phenomena such as an ICL injection during recent mergers of stars with average early-type spectra, the reversed star formation-density relation found at this high redshift in comparison with lower-redshift clusters, and projection effects.