2015ApJ...799...91Y

In the center of active galactic nuclei (AGNs), the dusty torus absorbs the radiation from the central engine and reemits in mid-infrared (MIR). Observations have detected moderate anisotropy in the dust MIR emission, in the way that type 1 AGNs (type1s) are mildly brighter in MIR comparing with type 2 sources (type2s). However, type1s and type2s were found to follow statistically the same tight MIR-hard X-ray correlation, suggesting that the MIR emission is highly isotropic assuming that the hard X-ray radiation is inclination independent. We argue that this discrepancy could be solved considering that the hard X-ray emission in AGNs is also mildly anisotropic, as we recently discovered. To verify this diagram, we compare the subarcsecond 12 µm flux densities of type1s and type2s using the [O IV] λ25.89 µm emission line as an isotropic luminosity indicator. We find that on average type1s are brighter in nuclei 12 µm radiation by a factor of 2.6±0.6 than type2s at given [O IV] λ25.89 µm luminosities, confirming the mild anisotropy of the nuclei 12 µm emission. We show that the anisotropy of the 12 µm emission we detected is in good agreement with radiative transfer models of clumpy tori. The fact that type1s and type2s follow the same tight MIR-hard X-ray correlation instead supports that both the MIR emission and hard X-ray emission in AGNs are mildly anisotropic.