The thermodynamic structure and large-scale structure filament in MACS J0717.5+3745

We present the results of Chandra and XMM-Newton X-ray imaging and spatially resolved spectroscopy, along with new MUSTANG2 90 GHz observations of the thermal Sunyaev-Zeldovich (SZ) effect on MACS J0717.5+3745. This exceptionally massive (3.5 ± 0.6 × 10 15 M ⊙ ) Frontier Fields cluster located at intermediate redshift ( z = 0.5458) is experiencing multiple mergers and hosting an apparent X-ray bright large-scale structure filament. We produced thermodynamical maps from Chandra, XMM-Newton, and ROSAT data using a new method to model the astrophysical and instrumental backgrounds. The temperature peak of 24 ± 4 keV is also the pressure peak of the cluster and it is spatially closely correlated with the SZ peak from the MUSTANG2 data. We characterised a potential shock candidate at the cluster centre, based on the sharp temperature and pressure gradient. We also quantified its temperature-derived Mach number in various directions to span a range of ℳ = (1.7 − 2.0)±0.3. We used Bayesian X-ray analysis methods to disentangle different projected spectral signatures for the filament structure, with the Akaike and Bayes information criteria (AIC and BIC) used to select the most appropriate model to describe the various temperature components. We report an X-ray filament temperature of 3.1 +0.6 −0.3 keV and a density (3.78 ± 0.05)×10 −4 cm −3 , corresponding to an overdensity of ∼400 relative to the critical density of the Universe. We estimate the hot gas mass of the filament to be ∼6.1 × 10 12 M ⊙ , while its total projected weak-lensing measured mass is ∼(6.8 ± 2.7)×10 13 M ⊙ , indicating a hot baryon fraction of 4–10%.

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