解析圆规星系活动核尘埃环的复杂结构
Resolving the complex structure of the dust torus in the active nucleus of the Circinus galaxy
摘要：
为了直接检验活动星系核的尘埃环模型，我们使用甚大望远镜干涉仪上的高分辨率干涉仪在中红外波段进行观测，研究了圆规星系核尘埃分布的范围和形态。我们发现，尘埃分布在Circinus的核心可以解释两个组件，一个密集和温暖的盘状组件的0.4 pc的大小和一个稍冷，几何厚环面组件的大小为2.0 pc。盘组件的方向垂直于电离锥和流出，似乎显示出在10微米的发射硅酸盐功能。它在方向和大小上与核微波激射盘一致。根据加热尘埃所需的能量，我们推断出吸积盘的光度相当于核黑洞爱丁顿光度的20%。我们发现，干涉数据是不一致的一个简单的，光滑的和轴对称的尘埃排放。尘埃粒子的不规则行为和尘埃温度随半径的浅度降低为尘埃结构提供了强有力的证据。我们没有看到尘埃再加工的证据，因为硅酸盐吸收曲线与标准星系尘埃一致。我们认为，电离辐射的准直必须起源于几何厚环面组件。我们的研究结果证实了存在一个几何厚，环面状尘埃分布在Circinus的核心，所需的塞弗特星系的统一计划。我们的数据的几个方面要求，这个环面是不规则的，或“cloudly”。
英文摘要：
To test the dust torus model for active galactic nuclei directly, we study the extent and morphology of the nuclear dust distribution in the Circinus galaxy using high resolution interferometric observations in the mid-infrared with the MIDI instrument at the Very Large Telescope Interferometer. We find that the dust distribution in the nucleus of Circinus can be explained by two components, a dense and warm disk-like component of 0.4 pc size and a slightly cooler, geometrically thick torus component with a size of 2.0 pc. The disk component is oriented perpendicular to the ionisation cone and outflow and seems to show the silicate feature at 10 micron in emission. It coincides with a nuclear maser disk in orientation and size. From the energy needed to heat the dust, we infer a luminosity of the accretion disk corresponding to 20% of the Eddington luminosity of the nuclear black hole. We find that the interferometric data are inconsistent with a simple, smooth and axisymmetric dust emission. The irregular behaviour of the visibilities and the shallow decrease of the dust temperature with radius provide strong evidence for a clumpy or filamentary dust structure. We see no evidence for dust reprocessing, as the silicate absorption profile is consistent with that of standard galactic dust. We argue that the collimation of the ionising radiation must originate in the geometrically thick torus component. Our findings confirm the presence of a geometrically thick, torus-like dust distribution in the nucleus of Circinus, as required in unified schemes of Seyfert galaxies. Several aspects of our data require that this torus is irregular, or "clumpy".
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