Nonthermal Emissions from a Head–Tail Radio Galaxy in 3D Magnetohydrodynamic Simulations

Abstract

We present magnetohydrodynamic simulations of a jet–wind interaction in a galaxy cluster and the radio to gamma-ray and neutrino emissions from this “head–tail galaxy.” Our simulation follows the evolution of cosmic-ray (CR) particle spectra with energy losses and stochastic turbulence acceleration. We find that the reacceleration is essential to explaining the observed radio properties of head–tail galaxies, in which the radio flux and spectral index do not drastically change. Our models suggest that hard X-ray emissions can be detected around the head–tail galaxy in the Perseus cluster by hard X-ray satellites, such as FORCE, and they will potentially constrain the acceleration efficiency. We also explore the origin of the collimated synchrotron threads, which have been found in some head–tail galaxies by recent high-quality radio observations. Thin and elongated flux tubes, connecting the two tails, are formed by strong backflows at an early phase. We find that these threads advect with the wind for over 300 Myr without disruption. The radio flux from the flux tubes is much lower than the typical observed flux. An efficient CR diffusion process along the flux tubes, however, may solve this discrepancy.