NGC 424 2型核极区秒差距尺度尘埃排放
Parsec-scale dust emission from the polar region in the type 2 nucleus of NGC 424
摘要：
在红外IR的进步开辟了可能性，空间解决活动星系核的秒差距尺度的水平和研究的环核尘埃分布，通常被称为“尘埃环”，这是负责1型/2型二分法的活动星系核。我们使用中红外光束组合器，结合VLTI的8米望远镜，观察了塞弗特2星系NGC 424的核，实现了可用望远镜配置几乎完全覆盖紫外平面。我们探测到扩展的中红外发射，其相对基线和模型独立的中红外半光半径为（2.0 \pm 0.2）pc \times（1.5 \pm 0.3）pc（在8-13 μm波长范围内平均）。扩展的中红外光源显示出随着波长增加的尺寸。位置角为-27度的主轴方向与光学偏振观察设置的系统轴紧密对齐。环面模型通常倾向于在中红外波长处沿中平面延伸。因此，我们得出结论，在这2型活动星系核的pc尺度的中红外辐射（>~60%）的大部分来源于光学薄的尘埃在活动星系核的极地地区，一个方案一致的近远红外SED。我们认为，一个辐射驱动的尘埃风，可能在一个膨胀的区域内热的一部分的环面，是负责极地尘埃。在这张照片中，环面主导了近红外辐射，直到约5 μm，而极地尘埃是中红外通量的主要贡献者。我们对NGC 424的研究结果与最近对圆规星系活动星系核的观测结果一致，并且与其他天体的大尺度特征相似。如果我们的结果反映了活动星系核的一般性质，那么目前解释和模拟活动星系核红外辐射的范式就必须加以修正。（节略）
英文摘要：
Advancements in infrared IR open up the possibility to spatially resolve AGN on the parsec-scale level and study the circumnuclear dust distribution, commonly referred to as the "dust torus", that is held responsible for the type 1/type 2 dichotomy of AGN. We used the mid-IR beam combiner MIDI together with the 8m telescopes at the VLTI to observe the nucleus of the Seyfert 2 galaxy NGC 424, achieving an almost complete coverage of the uv-plane accessible by the available telescope configurations. We detect extended mid-IR emission with a relatively baseline- and model-independent mid-IR half-light radius of (2.0 \pm 0.2) pc \times (1.5 \pm 0.3) pc (averaged over the 8-13 μm wavelength range). The extended mid-IR source shows an increasing size with wavelength. The orientation of the major axis in position angle -27deg is closely aligned with the system axis as set by optical polarization observations. Torus models typically favor extension along the mid-plane at mid-IR wavelengths instead. Therefore, we conclude that the majority of the pc-scale mid-IR emission (>~60%) in this type 2 AGN originates from optically-thin dust in the polar region of the AGN, a scenario consistent with the near- to far-IR SED. We suggest that a radiatively-driven dusty wind, possibly launched in a puffed-up region of the inner hot part of the torus, is responsible for the polar dust. In this picture, the torus dominates the near-IR emission up to about 5 μm, while the polar dust is the main contributor to the mid-IR flux. Our results of NGC 424 are consistent with recent observations of the AGN in the Circinus galaxy and resemble large-scale characteristics of other objects. If our results reflect a general property of the AGN population, the current paradigm for interpreting and modeling the IR emission of AGN have to be revised. (abridged)
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