Dissecting the RELICS cluster SPT-CLJ0615–5746 through intracluster light: Confirmation of the multiple merging state of the cluster formation

• Published in: Astronomy and astrophysics (Berlin) 2023-08, Vol.676, p.A39
• Main Authors: Jiménez-Teja, Y., Dupke, R. A., Lopes, P. A. A., Vílchez, J. M.
• Format: Article
• Language: English
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/202346580

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.