2022A&A...660A.112B

We present the characterisation of the massive cluster ClG J104803.7+313843 at z = 0.76 performed using a serendipitous XMM-Newton observation. High redshift and massive objects represent an ideal laboratory to benchmark our understanding of how clusters form and assembly formation is mainly driven by gravity. Leveraging the high throughput of XMM-Newton we were firstly able to determine the redshift of the object, shedding light on ambiguous photometric redshift associations. We investigated the morphology of this cluster which shows signs of merging activities in the outskirts and a flat core. We also measured the radial density profile up to R₅₀₀. With these quantities in hand, we were able to determine the mass, M₅₀₀=5.64_–0.62^+0.79x10¹⁴M_☉, using the Y_X proxy. This quantity improves the previous measurement of the mass of this object by a factor of ∼3.5. The characterisation of one cluster at such a mass and redshift regime is fundamental as these objects are intrinsically rare, with the number of objects discovered so far being less than ∼25. Our study highlights the importance of using X-ray observations in combination with ancillary multi-wavelength data to improve our understanding of high-z and massive clusters.