Flow Dynamics and Radio Morphology of FR-I Jets

Abstract

Flow Dynamics and Radio Morphology of FR-I Jets

Hyesung Kang (Pusan National University, Korea) Ayan Bhattacharjee (UNIST, Korea) Dongsu Ryu (UNIST, Korea) Jeongbhin Seo (UNIST, Korea)

Radio galaxies are typically classified into two main categories based on their morphology: center-brightened FR-I and edge-brightened FR-II. The jet power and its interactions with the surrounding medium are thought to play a crucial role in the deceleration and decollimation of the jet-spine flows, which contribute to this classification. Through high-resolution, three-dimensional relativistic hydrodynamic simulations, we investigate the development of flow structures on sub-kpc to kpc scales in kinetically dominant, low-power relativistic jets. Our findings indicate that the dynamics and structures of jet-induced flows are primarily influenced by the bulk Lorentz factor of the jet spine and the advance speed of the jet head, which depend on energy injection flux and the contrast between jet and background density. The entrainment of ambient gas, as well as the background density and pressure gradients, also contribute significantly to these dynamics. To replicate radio morphology, we generate synthetic maps of the synchrotron surface brightness for the simulated jets using simplified models for magnetic field distribution and nonthermal electron populations, factoring in relativistic beaming effects at different inclination angles. Both the flow structures and radio maps reflect the longitudinal and transverse features of the jet-spine and shear layer, consistent with observational data. Additionally, we compare various background effects and suggest that the loss of pressure confinement beyond the galactic core may be a key factor in the flaring and disruption of FR-I jets. Our results support the idea that mildly relativistic jets can explain the observed asymmetries and one-sidedness, with the main jet being boosted and the counterjet deboosted.