A new observation-based clumpy torus model for activate galactic nuclei

Abstract

The obscuration observed in active galactic nuclei (AGN) is mainly caused by dust and gas distributed in a torus-like structure surrounding the supermassive black hole (SMBH). Recent observations suggest that the obscuring material in the dusty torus is clumpy rather than uniformly distributed. However, most of the AGN models still adopt a smooth torus when characterizing obscuring material surrounding the SMBH. In this work, we perform a broadband X-ray spectral analysis of a large unbiased sample of obscured AGN in the nearby universe which have high-quality archival NuSTAR data, enabling us to accurately characterize the physical and geometrical properties of their obscuring tori. We find that different types of AGN may possess similar tori, which are on average Compton thick (NH,tor,ave~1.4x10^24 cm^-2 ) and are significantly clumpy (e.g., for >80% of sources in our sample, their torus average column densities are more than three times different from their line-of-sight column densities). Utilizing the obtained information about the torus column density, torus covering factor, and torus clumpiness for all sources in our sample, we develop a new clumpy torus model of AGN. Using our new model, we predict the observed column density distribution of AGN in the nearby universe, which we find in good agreement with the constraints from recent population synthesis models.