The properties of magnetised cold filaments in a cool-core galaxy cluster

¹ Universität Hamburg, Hamburger Sternwarte, Gojenbergsweg 112, 21029, Hamburg, Germany
² Department of Computational Mathematics, Science, and Engineering, Michigan State University, East Lansing, MI 48824, USA
³ Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA
⁴ Facility for Rare Isotope Beams, Michigan State University, East Lansing, MI 48824, USA

^⋆ Corresponding author; martin.fournier@hs.uni-hamburg.de

Received: 7 June 2024
Accepted: 31 August 2024

Abstract

Context. Filaments of cold gas (T ≤ 10⁴ K) are found in the inner regions of many cool-core clusters. These structures are thought to play a major role in the regulation of feedback from active galactic nuclei (AGNs).

Aims. We study the morphology of the filaments, their formation, and their impact on the propagation of the outflowing AGN jets.

Methods. We present a set of GPU-accelerated 3D magnetohydrodynamic simulations of an idealised Perseus-like cluster using the performance portable code ATHENAPK. We include radiative cooling and a self-regulated AGN feedback model that redistributes accreted material through kinetic, thermal, and magnetic feedback.

Results We confirm that magnetic fields play an important role in both the formation and evolution of the cold material. These suppress the formation of massive cold discs and favour magnetically supported filaments over clumpy structures. Achieving resolutions of 25 − 50 pc, we find that filaments are not monolithic as they contain numerous and complex magnetically supported sub-structures. We find that the mass distribution of these clumps follows a power law of slope of ∼ − 0.6 for all investigated filaments. Studying the evolution of individual filaments, we find that their formation pathways can be diverse. We find examples of filaments forming through a combination of gas uplifting and condensation, as well as systems of purely infalling clumps condensing out of the intracluster medium. The density contrast between the cold gas and the outflowing hot material leads to recurring deflections of the jets, favouring inflation of bubbles.

Conslusions. Filaments in cool-core clusters are clumpy and contain numerous sub-structures, resulting from a complex interplay between magnetic fields, thermal instability, and jet-cloud interaction. Frequent deflections of the AGN outflows suppress jet collimation and favour the formation of large X-ray bubbles, and smaller off-axis cavities.