Dust around active galactic nuclei ( AGN ) is distributed over a wide range of spatial scales and can be observed in the infrared ( IR ) .
It is generally assumed that the distribution on parsec scales forms a geometrically- and optically-thick entity in the equatorial plane around the accretion disk and broad-line region – dubbed “ dust torus ” – that emits the bulk of the sub-arcsecond-scale IR emission and gives rise to orientation-dependent obscuration .
However , recent IR interferometry studies with unprecedented position angle and baseline coverage on these small scales in two obscured ( type 2 ) AGN have revealed that the majority of the mid-IR emission in these objects is elongated in polar direction .
These observations are difficult to reconcile with the standard interpretation that most of the parsec-scale mid-IR emission in AGN originates from the torus and challenges the justification of using simple torus models to model the broad-band IR emission .
Here we report detailed interferometry observations of the unobscured ( type 1 ) AGN in NGC 3783 that allow us to constrain the size , elongation , and direction of the mid-IR emission with high accuracy .
The mid-IR emission is characterized by a strong elongation toward position angle PA -52 ^ { \circ } , closely aligned with the polar axis ( PA -45 ^ { \circ } ) .
We determine half-light radii along the major and minor axes at 12.5 \micron of ( 20.0 \pm 3.0 ) \mathrm { mas } \times ( 6.7 \pm 1.0 ) \mathrm { mas } or ( 4.23 \pm 0.63 ) \mathrm { pc } \times ( 1.42 \pm 0.21 ) \mathrm { pc } , which corresponds to intrinsically-scaled sizes of ( 69.4 \pm 10.8 ) r _ { \mathrm { in } } \times ( 23.3 \pm 3.5 ) r _ { \mathrm { in } } for the inner dust radius of r _ { \mathrm { in } } = 0.061 pc as inferred from near-IR reverberation mapping .
This implies an axis ratio of 3:1 , with about 60 - 90 % of the 8 - 13 \micron emission associated with the polar-elongated component .
It is quite likely that the hot-dust emission as recently resolved by near-IR interferometry is misaligned with the mid-IR emitting source , which also finds a correspondence in the two distinct 3 - 5 \micron and 20 \micron bumps seen in the high-angular resolution spectral energy distribution ( SED ) .
Based on this SED , we determine covering factors for the hot and warm dust components of C _ { \mathrm { hot } } = 0.42 ^ { +0.42 } _ { -0.21 } and C _ { \mathrm { warm } } = 0.92 ^ { +0.92 } _ { -0.46 } , respectively .
We conclude that these observations support a scenario that the majority of the mid-IR emission in Seyfert AGN originates from a dusty wind in the polar region of the AGN .