2021A&A...653A.163K

We conducted an X-ray analysis of one of the two Planck-detected triplet-cluster systems, PLCK G334.8-38.0, with a ∼100ks deep XMM-Newton data. We find that the system has a redshift of z=0.37±0.01 but the precision of the X-ray spectroscopy for two members is too low to rule out a projected triplet system, demanding optical spectroscopy for further investigation. In projection, the system looks almost like an equilateral triangle with an edge length of ∼2.0Mpc, but masses are very unevenly distributed (M₅₀₀~[2.5, 0.7, 0.3]x10¹⁴M_☉ from bright to faint). The brightest member appears to be a relaxed cool-core cluster and is more than twice as massive as both other members combined. The second brightest member appears to be a disturbed non-cool-core cluster and the third member was too faint to make any classification. None of the clusters have an overlapping R₅₀₀ region and no signs of cluster interaction were found; however, the XMM-Newton data alone are probably not sensitive enough to detect such signs, and a joint analysis of X-ray and the thermal Sunyaev-Zeldovich effect is needed for further investigation, which may also reveal the presence of the warm-hot intergalactic medium within the system. The comparison with the other Planck-detected triplet-cluster-system (PLCK G214.6+36.9) shows that they have rather different configurations, suggesting rather different merger scenarios, under the assumption that they are both not simply projected triplet systems.