Investigating the magnetic field in the inter-cluster filament between Abell 3667 and Abell 3651 with POSSUM

@misc{stuardi2026investigating,
  title = {{Investigating the magnetic field in the inter-cluster filament between Abell 3667 and Abell 3651 with POSSUM}},
  author = {C. Stuardi and S. P. O'Sullivan and L. Rudnick and G. Bernardi and A. Bonafede and J. Dietl and T. Akahori and D. Alonso-López and C. Anderson and E. Carretti and B. M. Gaensler and G. Heald and F. Loi and Y. K. Ma and E. Osinga and G. Pignataro and C. Riseley and X. Sun and A. Thomson and C. L. Van Eck and T. Vernstrom and J. L. West},
  howpublished = {arXiv},
  year = {2026},
  month = aug,
  doi = {10.48550/arxiv.2608.28758},
  eprint = {2608.28758},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2608.28758},
}

TY  - UNPB
TI  - Investigating the magnetic field in the inter-cluster filament between Abell 3667 and Abell 3651 with POSSUM
AU  - C. Stuardi
AU  - S. P. O'Sullivan
AU  - L. Rudnick
AU  - G. Bernardi
AU  - A. Bonafede
AU  - J. Dietl
AU  - T. Akahori
AU  - D. Alonso-López
AU  - C. Anderson
AU  - E. Carretti
AU  - B. M. Gaensler
AU  - G. Heald
AU  - F. Loi
AU  - Y. K. Ma
AU  - E. Osinga
AU  - G. Pignataro
AU  - C. Riseley
AU  - X. Sun
AU  - A. Thomson
AU  - C. L. Van Eck
AU  - T. Vernstrom
AU  - J. L. West
PY  - 2026
DA  - 2026/08/28
PB  - arXiv
DO  - 10.48550/arxiv.2608.28758
UR  - https://arxiv.org/abs/2608.28758
AB  - [Abridged abstract] The objective of this study is to measure the magnetic field within the prominent inter-cluster filament recently detected in X-rays by the extended ROentgen Survey with an Imaging Telescope Array (eROSITA). This filament spans over 13 Mpc projected on the sky, connecting the galaxy clusters Abell 3667 and Abell 3651. We employed the Polarisation Sky Survey of the Universe's Magnetism (POSSUM) Rotation Measure (RM) grid to isolate the RM dispersion and median value of background polarised sources induced by the filament's magnetised plasma, and to infer the strength of this magnetic field. The filament region is sampled by 54 background polarised sources. After subtracting the foreground Galactic RM, we detected a marginal residual RM dispersion in the filament region of 6.9±3.6 rad/m^2, together with a coherent residual RM signal with median 6.3±1.3 rad/m^2. Assuming simplified single-scale magnetic-field models and adopting informed priors on the thermal electron density distribution derived from the X-ray analysis, we constrained the magnetic field strength to the range 0.1-3.5 μG within 95% confidence, with preferred values around 0.2-0.3 μG depending on the assumed magnetic-field coherence scale. However, we also found that the Galactic foreground RM in this region is highly structured on angular scales comparable to the extent of the filament itself, representing a major source of uncertainty for the RM analysis. Our results provide the first magnetic field constraints based on Faraday rotation measurements in an individual X-ray-detected inter-cluster filament, with field strengths consistent with theoretical expectations for gas in bridges and cluster outskirts. Our analysis also highlights the critical importance of accurately modelling Galactic RM foregrounds for future studies of extra-galactic magnetism with POSSUM and the SKA.
ER  -