Dynamic and radiative implications of jet–star interactions in AGN jets

Abstract

Context. The interactions between jets from active galactic nuclei (AGN) and their stellar environments significantly influence jet dynamics and emission characteristics. In low-power jets, such as those in Fanaroff-Riley I (FR I) galaxies, the jet–star interactions can notably affect jet deceleration and energy dissipation. Aims. Recent numerical studies suggest that mass loading from stellar winds is a key factor in decelerating jets, accounting for many observed characteristics in FR I jets. Additionally, a radio-optical positional offset has been observed, with optical emission detected further down the jet than radio emission. This observation may challenge traditional explanations based solely on recollimation shocks and instabilities. Methods. We used the radiative transfer code RIPTIDE to generate synthetic synchrotron maps from a population of re-accelerated electrons in both radio and optical bands from jet simulations incorporating various mass-loading profiles and distributions of gas and stars within the ambient medium. Results. Our findings emphasize the importance of mass entrainment in replicating the extended and diffuse radio/optical emissions observed in FR I jets and in explaining the radio–optical offsets. These offsets are influenced by the galaxy's physical properties, the surrounding stellar populations, and observational biases. We successfully reproduce typical radio–optical offsets by considering a mass-loading equivalent to 10^‑9 M_⊙ ṡ yr^‑1 ṡ pc^‑3. Overall, our results demonstrate that positive offset measurements are a promising tool for revealing the fundamental properties of galaxies and potentially their stellar populations, particularly in the context of FR I jets.