Synchrotron emission from elliptical galaxies consequent to active galactic nucleus outbursts

Both radiative and mechanical feedback from active galactic nuclei have been found to be important for the evolution of elliptical galaxies. We compute how a shock may be driven from a central black hole into the gaseous envelope of an elliptical galaxy by such feedback (in the form of nuclear winds) using high resolution one-dimensional hydrodynamic simulations. We calculate the synchrotron emission from the electron cosmic rays accelerated by the shocks (not the jets) in the central part of elliptical galaxies, and we also study the synchrotron spectrum's evolution using the standard diffusive shock acceleration mechanism, which is routinely applied to supernova remnants. We find quantitative consistency between the synchrotron radio emission produced via this mechanism with extant observations of elliptical galaxies which are undergoing outbursts. Additionally, we also find that synchrotron optical and X-ray emission can co-exist inside elliptical galaxies during a specific evolutionary phase subsequent to central outbursts. In fact, our calculations predict a peak synchrotron luminosity of ∼1.3 × 10⁶ L _⊙ at the frequency 5 GHz (radio band), of ∼1.1 × 10⁶ L _⊙ at 4.3 × 10¹⁴Hz (corresponding to the absolute magnitude -10.4 in R band), and of ∼1.5 × 10⁷ L _⊙ at 2.4 × 10¹⁷Hz (soft X-ray, 0.5-2.0 keV band).