Exemplary Merging Clusters II: XMM-Newton and Chandra X-ray Observations of MACS J1752.0+4440 and ZwCl 1856.8+6616
Using deep XMM-Newton and Chandra observations, we compare the double-radio-relic galaxy cluster mergers MACS J1752.0+4440 and ZwCl 1856.8+6616. Both are 1:1 mass-ratio mergers with similar relic separations but differing nearly an order of magnitude in total mass. In MACS J1752.0+4440, the surface-brightness discontinuity at the northeastern relic yields Mach $M_ρ=1.4\pm0.2$, while the temperature jump provides a weaker constraint, corresponding to $M_{kT}\lesssim2.3$ at the $2σ$ level, lower than the radio-derived $M_{\rm radio}=3.1\pm0.1$. No discontinuity is detected at the southwestern relic. Thermodynamic maps and axial profiles reveal surviving relatively low-entropy cores embedded in Mpc-scale stripped-gas structures. The nearly uniform X-ray tail brightness and a southwestern plateau coincident with a third lensing mass peak favor a non-zero impact parameter and complex assembly history. In ZwCl 1856.8+6616, we do not detect a clear surface brightness discontinuity at either relic. The northern X-ray peak leads its brightest cluster galaxy (BCG) and lensing peak, while the hotter southern X-ray peak is laterally offset from its BCG and lensing peak. The asymmetric intracluster emission favors a phase near or after first apocenter, when displaced gas can develop a slingshot-like morphology. We present two TNG-Cluster analogs in which a minor merger followed by an off-axis major collision produces extended X-ray tails resembling MACS J1752.0+4440 and later leads to gas structures resembling ZwCl 1856.8+6616. X-ray morphology independently confirms the merger phases inferred from relic-based chronometry, placing MACS J1752.0+4440 before and ZwCl 1856.8+6616 after first apocenter, and demonstrating that similar relic and lensing configurations can correspond to distinct dynamical states.