Radio signatures of AGN-wind-driven shocks in elliptical galaxies: From simulations to observations

TL;DR

This study models the synchrotron radio emission from shocks driven by AGN winds in elliptical galaxies using simulations, predicting observable signatures that can help detect AGN feedback effects.

Contribution

It introduces a simulation-based framework to predict radio signatures of AGN wind-driven shocks, connecting theoretical models with potential observations.

Findings

Shocks produce radio luminosities around 10^{29} erg s^{-1} Hz^{-1}.

Spectral indices range from -0.4 to -1.4, steepening over time.

Model matches observed radio features in galaxy M32.

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 $10^{29}\,\mathrm{erg\,s^{-1}\,Hz^{-1}}$ in the radio band (0.5-5 GHz), with spectral indices of $\alpha \approx -0.4$ 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.