3D radiative transfer modelling of the dusty tori around active galactic nuclei as a clumpy two-phase medium

Abstract

We investigate the emission of active galactic nuclei (AGN) dusty tori in the infrared domain. Following theoretical predictions coming from hydrodynamical simulations, we model the dusty torus as a 3D two-phase medium with high-density clumps and low-density medium filling the space between the clumps. Spectral energy distributions (SED) and images of the torus at different wavelengths are obtained using 3D Monte Carlo radiative transfer code SKIRT. Our approach of generating clumpy structure allows us to model tori with single clumps, complex structures of merged clumps or interconnected sponge-like structure. A corresponding set of clumps-only models and models with smooth dust distribution is calculated for comparison. We found that dust distribution, optical depth, clump size and their actual arrangement in the innermost region, all have an impact on the shape of near- and mid-infrared SED. The 10 micron silicate feature can be suppressed for some parameters, but models with smooth dust distribution are also able to produce a wide range of the silicate feature strength. Finally, we find that having the dust distributed in a two-phase medium, might offer a natural solution to the lack of emission in the near-infrared, compared to observed data, which affects clumpy models currently available in the literature.