Ensemble mapping the inner structure of luminous quasars

Abstract

ABSTRACT A simple prediction of the well-known unification model of active galactic nuclei is that a sample of sources should exhibit an anticorrelation between the solid angle of the dusty torus and of the ionization cone (as the sum of them shall equal 4π); however, this has never been detected. In this work, we analyse the correlation between the [O iii] 5007 narrow emission line equivalent width and LIR(λ)/Lbol for a large sample of luminous quasars. For the first time, we detect a clear intrinsic anticorrelation between them, which immediately verifies the torus/ionization-cone geometry in luminous quasars. More interestingly, the anticorrelation significantly weakens with increasing wavelength from ∼2 to 12 $\mu$m, and disappears at ∼12 $\mu$m. Simulations show that a cool dust component (in addition to the equatorial torus) with its strength positively correlating with the solid angle of the ionization cone is required to explain the observations. This shows that the polar dust seen in nearby active galaxies also exists in luminous quasars, with its contribution to total dust emission increasing with λ (from ∼2 to 12 $\mu$m) and reaching between 39 per cent and 62 per cent (model dependent) at rest frame 12 $\mu$m. Our findings provide a unique approach to map the otherwise spatially unresolvable inner structure of quasars.