Formation of giant radio sources in galaxy clusters

¹ School of Physics, Henan Normal University, Xinxiang 453007, People’s Republic of China
² Center for Theoretical Physics, Henan Normal University, Xinxiang 453007, People’s Republic of China
³ Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, People’s Republic of China
⁴ Department of Astronomy, School of Physics and Astronomy, Key Laboratory of Astroparticle Physics of Yunnan Province, Yunnan University, Kunming 650091, People’s Republic of China

^⋆ Corresponding authors: duanxiaodong@htu.edu.cn; zhangruiyu@htu.edu.cn; wulinhui@shao.ac.cn

Received: 6 October 2024
Accepted: 29 March 2025

Abstract

Context. The number of observed giant radio sources (GRSs) has increased significantly in recent years, yet their formation mechanisms remain elusive. The discovery of giant radio galaxies within galaxy clusters has further intensified the ongoing debates.

Aims. We focus on the impact of jet properties, including jet power, energy components, and magnetic field structure, on the formation of GRSs within galaxy clusters.

Methods. We utilized magnetohydrodynamic simulations to investigate the formation of GRSs in cluster environments. To avoid confusing the effects of power and total energy injection, we held the energy of jet outbursts fixed and studied the effect of power by varying the active duration of the jets. Furthermore, we examined the roles of magnetic, thermal, and kinetic energy components by adjusting their fractions in the jets. Additionally, we calculated radio emission for comparison with observations in the radio power-linear size diagram (P-D diagram). Finally, we also studied the energy transport processes of different jets.

Results. We find the “lower power-larger bubble” effect: when the total jet energy is fixed, low-power jets tend to produce larger radio sources. Regarding different energy components, jets dominated by toroidal magnetic field energy generate larger radio sources than kinetic and thermal energy-dominated jets. Conversely, strong poloidal magnetic fields hinder radio lobe growth. When injecting 2.06 × 10⁵⁹ erg into a 10¹⁴ solar mass halo, only jets with powers of approximately 10⁻⁴–10⁻³ Eddington luminosity efficiently traverse the observational region in the P-D diagram.

Conclusions. Our findings suggest that energetic, long-lasting (low-power), continuous jets endowed with significant toroidal magnetic fields facilitate the formation of GRSs in cluster environments. However, although jets with significantly lower power can generate substantially larger radio sources, their faintness may render them unobservable.