The primary source of emission of active galactic nuclei ( AGN ) , the accretion disk , is surrounded by an optically and geometrically thick dusty structure ( “ the so-called dusty torus ” ) .
The infrared radiation emitted by the dust is nothing but a reprocessed fraction of the accretion disk emission , so the ratio of the torus to the AGN luminosity ( L _ { \text { torus } } / L _ { \text { AGN } } ) should correspond to the fraction of the sky obscured by dust , i.e .
the covering factor .
We undertook a critical investigation of the L _ { \text { torus } } / L _ { \text { AGN } } as the dust covering factor proxy .
Using state-of-the-art 3D Monte Carlo radiative transfer code , we calculated a grid of spectral energy distributions ( SEDs ) emitted by the clumpy two-phase dusty structure .
With this grid of SEDs , we studied the relation between L _ { \text { torus } } / L _ { \text { AGN } } and the dust covering factor for different parameters of the torus .
We found that in the case of type 1 AGNs the torus anisotropy makes L _ { \text { torus } } / L _ { \text { AGN } } underestimate low covering factors and overestimate high covering factors .
In type 2 AGNs L _ { \text { torus } } / L _ { \text { AGN } } always underestimates covering factors .
Our results provide a novel easy-to-use method to account for anisotropy and obtain correct covering factors .
Using two samples from the literature , we demonstrated the importance of our result for inferring the obscured AGN fraction .
We found that after the anisotropy is properly accounted for , the dust covering factors show very weak dependence on L _ { \text { AGN } } , with values in the range of \approx 0.6 - 0.7 .
Our results also suggest a higher fraction of obscured AGNs at high luminosities than those found by X-ray surveys , in part owing to the presence of a Compton-thick AGN population predicted by population synthesis models .