Collisions among Clouds inside Dusty Torus in Active Galactic Nuclei: Observational Consequences

Abstract

A geometrically thick dusty torus in NGC 1068 has been unambiguously resolved by an infrared interferometry telescope. This implies clouds composing the dusty torus are undergoing supersonic collisions with each other. We show that the collisions form strong non-relativistic shocks, which accelerate populations of relativistic electrons. Torus reprocesses emission from accretion disk into infrared band. We show that the energy density of the infrared photons inside the torus is much higher than that of the magnetic field in the clouds and the seed photons of inverse Compton scattering are mainly from the infrared ones. The maximum energy of the relativistic electrons can reach a Lorentz factor of $10^5$. We calculate the spectrum of the synchrotron and inverse Compton scattering radiation from the electrons in the torus. The relativistic electrons in the torus radiate non-thermal emission from radio to $\gamma$-ray, which isotropically diffuses in the region of the torus. We find the most prominent character is a peak at $\sim 0.5-1$ GeV. We apply this model to NGC 1068 and find that the observed radio emission from the core component $S_1$ can be explained by the synchrotron emission from the relativistic electrons. We predict that there is a $\gamma$-ray emission with a luminosity of $10^{40}$ erg/s peaking at $\sim 1$ GeV from the torus, which could be detected by {\em Gamma-Ray Large-Array Space Telescope} in the future. This will provide a new clue to understand the physics in the torus. The non-thermal radiation from dusty torus may explain the radio emission from Seyfert galaxies. The cosmological implications of the non-thermal emission to the $\gamma$-ray background radiation have been discussed.