极地地区的尘埃是AGN的IR排放的主要贡献者
Dust in the polar region as a major contributor to the IR emission of AGN
摘要：
一般认为，在秒差距尺度上的尘埃分布在赤道平面上围绕着吸积盘和宽线区域形成了一个几何和光学厚度的实体--被称为“尘埃环”--它发射出大部分亚弧秒尺度的红外辐射，并产生了与方向有关的遮蔽。在这里，我们报告了详细的干涉测量观测的未被掩盖的（1型）活动星系核在NGC 3783，使我们能够约束的大小，伸长率，和方向的中红外发射的高精度。中红外发射的特征在于朝向与极轴（PA-45度）紧密对准的位置角PA-52度的强伸长。我们确定了在12.5 μm处沿长轴和短轴的半光半径，（4.23 +/- 0.63）个x（1.42 +/- 0.21）个百分点，其对应于（69.4 +/- 10.8）rin x（23.3 +/- 3.5）rin，根据近红外混响映射推断，rin的内部尘埃半径= 0.061 pc。这意味着轴比为3：1，其中约60-90%的8-13 μm发射与极伸长分量有关。这些观测结果很难与活动星系核中绝大多数秒差距尺度的中红外辐射来源于环面的标准解释相一致，并对使用简单环面模型来模拟宽带红外辐射的合理性提出了挑战。最近通过近红外干涉测量法分辨出的NGC 3783中的热尘发射很可能与中红外发射源不一致，这也发现了在高角分辨率光谱能量分布（SED）中看到的两个不同的3-5 μm和20 μm隆起的对应关系。我们的结论是，这些意见支持的场景中，大多数的中红外辐射在塞弗特活动星系核起源于极地地区的活动星系核的尘埃风。
英文摘要：
(abridged) It is generally assumed that the distribution of dust 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. 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 deg, closely aligned with the polar axis (PA -45 deg). We determine half-light radii along the major and minor axes at 12.5 μm of (4.23 +/- 0.63) pc x (1.42 +/- 0.21) pc, which corresponds to intrinsically-scaled sizes of (69.4 +/- 10.8) rin x (23.3 +/- 3.5) rin for the inner dust radius of rin = 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 μm emission associated with the polar-elongated component. 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. It is quite likely that the hot-dust emission in NGC 3783 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 μm and 20 μm bumps seen in the high-angular resolution spectral energy distribution (SED). We conclude that these observations support a scenario where the majority of the mid-IR emission in Seyfert AGN originates from a dusty wind in the polar region of the AGN.
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