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

¹ Department of Theoretical Physics and Astrophysics, Masaryk University, Kotlářská 2, Brno 611 37, Czech Republic
² Department of Physics, Graduate School of Advanced Science and Engineering, Hiroshima University Kagamiyama, 1-3-1 Higashi-Hiroshima 739-8526, Japan
³ NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771, USA
⁴ Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
⁵ ESA/ESTEC, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
⁶ Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) No. 1 Section 4 Roosevelt Road Taipei 106216 Taiwan
⁷ SRON Netherlands Institute for Space Research, Niels Bohrweg 4, 2333 CA Leiden, The Netherlands
⁸ Leiden Observatory Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁹ Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo, Kashiwa, Chiba, 277-8583, Japan
¹⁰ University of Pennsylvania, 209 S. 33rd St., Philadelphia, PA 19014, USA
¹¹ Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 AD, Groningen, The Netherlands
¹² Laboratoire Lagrange, Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Blvd de l’Observatoire, CS 34229, 06304 Nice cedex 4, France
¹³ Department of Physics, McGill University, 3600 University Street Montreal, QC H3A 2T8, Canada
¹⁴ National Radio Astronomy Observatory, 520 Edgemont Rd., Charlottesville, VA 22903, USA
¹⁵ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching bei München, Germany
¹⁶ Center for Astrophysics, Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
¹⁷ Department of Astronomy, University of Virginia, P.O. Box 400325 Charlottesville, VA 22904, USA

^⋆ Corresponding author: jeanpaul.breuer@gmail.com

Received: 6 November 2024
Accepted: 23 September 2025

Abstract

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 × 10¹⁵ 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 × 10¹² M_⊙, while its total projected weak-lensing measured mass is ∼(6.8 ± 2.7)×10¹³ M_⊙, indicating a hot baryon fraction of 4–10%.