[论文解读] Simulating cosmic ray electron spectra and radio emission from an AGN jet outburst in a cool-core cluster

Léna Jlassi, Rainer Weinberger+4 more|arXiv (Cornell University)|Jan 15, 2026

Astrophysics and Cosmic Phenomena被引用 0

一句话总结

作者将3D MHD AGN喷流模拟与亚网格宇宙射线电子模型（通过 Crest）及后处理的同步辐射发射代码（Crayon+）耦合，以研究 Perseus 类冷核团簇中的非热光谱和射电发射。

ABSTRACT

Active galactic nucleus (AGN) powered jets can accelerate cosmic ray electrons, leading to the observed radio synchrotron emission. To simulate this emission, jet dynamics in galaxy clusters must be coupled to electron spectral modelling. We run magneto-hydrodynamic (MHD) simulations of a single AGN jet outburst in a Perseus-like galaxy cluster and adopt a sub-grid model for the acceleration of cosmic ray protons and electrons at unresolved internal shocks in the jet. We evolve cosmic ray electron spectra along Lagrangian trajectories using the Fokker-Planck solver Crest and compute the non-thermal emission using Crayon+. The resulting total electron spectrum reaches a steady-state slope at high momenta, with a gradually decreasing normalization over time, while the lower-momentum portion continues to resemble a freely cooling spectrum. The interaction of the jets with the turbulent cluster environment inflates lobes which rise buoyantly, induce amplification of the magnetic fields and uplift old cosmic ray populations in the wake of the bubbles. We connect radio spectral indices to electron injection ages: at a given radio frequency, weaker magnetic fields are illuminated by higher momenta electrons, whose age is determined by the last injection event. On the other hand, stronger magnetic fields are illuminated by lower momenta electrons, whose age is determined by the maximum energy injection event in the past. This powerful approach allows us to relate the underlying MHD properties to electron spectra and the resulting radio synchrotron emission, thereby enabling us to infer the underlying physics from observed radio properties.

研究动机与目标

• Motivate the study of non-thermal emission from AGN jets as a probe of jet–ICM interaction and cooling-flow regulation in cool-core clusters.
• Develop and implement sub-grid acceleration of cosmic ray protons and electrons within AGN jets in a 3D MHD framework.
• Evolve cosmic ray electron spectra along Lagrangian tracer trajectories using a Fokker-Planck solver and connect spectra to observable radio emission.
• Investigate how jet activity, adiabatic processes, and mixing with the ICM shape electron spectra and their synchrotron signatures.

提出的方法

• Run 3D magneto-hydrodynamic simulations with Arepo of a single 50 Myr AGN jet outburst in a Perseus-like cluster.
• Adopt a sub-grid model to accelerate cosmic ray protons and electrons at unresolved internal shocks in the jet (CRp energy fraction fixed by an exponential injection).
• Evolve cosmic ray electron spectra along Lagrangian tracer trajectories using the Crest Fokker-Planck solver with adiabatic, Coulomb, and radiative losses.
• Inject a secondary CRe population in jet regions with a defined acceleration efficiency and a power-law injection spectrum upon jet conditions.
• Compute instantaneous non-thermal emission with Crayon+ by integrating the evolved electron spectra over the local magnetic field to obtain radio synchrotron emissivity.

实验结果

研究问题

• RQ1 How does a single AGN jet outburst in a cool-core cluster shape the evolution of cosmic ray electron spectra over hundreds of Myr?
• RQ2 How do adiabatic compression, dilution from mixing, and jet–ICM interactions influence the normalization and shape of the CRe spectrum?
• RQ3 How are the resulting radio synchrotron properties (spectral indices) linked to electron injection ages and magnetic field evolution?
• RQ4 To what extent can the combined MHD dynamics and sub-grid acceleration reproduce observed radio features and aging signatures in cluster jets?

主要发现

• The total cosmic ray electron spectrum reaches a steady-state slope at high momenta, with a gradually decreasing normalization over time.
• Lower-momentum electrons continue to resemble a freely cooling spectrum, reflecting ongoing radiative and Coulomb losses.
• Jet-inflated lobes rise buoyantly, amplify magnetic fields, and uplift old CR populations in the wake of bubbles.
• Radio spectral indices can be interpreted in terms of electron injection ages, with field strength governing which energy electrons illuminate which ages.
• The framework links underlying MHD properties to electron spectra and radio emission, enabling inference of jet–ICM physics from observations.