Radio signatures of AGN-wind-driven shocks in elliptical galaxies

From simulations to observations

¹ Astrophysics Division, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, P.R. China
² University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing 100049, P.R. China
³ Center for Astronomy and Astrophysics and Department of Physics, Fudan University, Shanghai 200438, P.R. China
⁴ School of Astronomy and Space Science, Nanjing University, Nanjing 210023, P.R. China
⁵ Key Laboratory of Modern Astronomy and Astrophysics, Nanjing University, Nanjing 210023, P.R. China
⁶ National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Beijing 100101, P.R. China

^⋆ Corresponding author: fyuan@fudan.edu.cn

Received: 15 July 2025
Accepted: 20 October 2025

Abstract

We investigate the synchrotron emission signatures of shocks driven by active galactic nucleus (AGN) wind in elliptical galaxies based on our two-dimensional axisymmetric hydrodynamic MACER numerical simulations. Using these simulation data, we calculate the synchrotron radiation produced by nonthermal electrons accelerated at shocks, adopting reasonable assumptions for the magnetic field and relativistic electron distribution (derived from diffusive shock acceleration theory), and predict the resulting observational signatures. In our fiducial model, shocks driven by AGN winds produce synchrotron emission with luminosities of approximately 10²⁹ erg s⁻¹ Hz⁻¹ in the radio band (0.5–5 GHz), with spectral indices of α ≈ −0.4 to −0.6 during the strongest shock phases, gradually steepening to about −0.8 to −1.4 as the electron population ages. Spatially, the emission is initially concentrated in regions of strong shocks, later expanding into more extended, diffuse structures. We also apply our model to the dwarf elliptical galaxy Messier 32 (M32), and find remarkable consistency between our simulated emission and the observed nuclear radio source, suggesting that this radio component likely originates from hot-wind-driven shocks. Our results indicate that AGN winds not only influence galaxy gas dynamics through mechanical energy input but also yield direct observational evidence via nonthermal radiation. With the advent of next-generation radio facilities such as the FAST Core Array, SKA, and ngVLA, these emission signatures serve as important probes for detecting and characterizing AGN feedback.