RADIATION-DRIVEN FOUNTAIN AND ORIGIN OF TORUS AROUND ACTIVE GALACTIC NUCLEI
RADIATION-DRIVEN FOUNTAIN AND ORIGIN OF TORUS AROUND ACTIVE GALACTIC NUCLEI
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DOI：
10.1088/0004-637x/758/1/66
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发表时间：
2012-08
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影响因子：
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通讯作者：
K. Wada
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作者：
K. Wada
我们提出了一个合理的机制来解释形成的所谓的模糊环面周围的活动星系核（AGN）的三维流体动力学模拟的基础上，包括从中央源的辐射反馈。用射线追踪法计算了X射线对气体的加热和辐射压力。这种辐射反馈驱动了一个“喷泉”，也就是说，在中心几到几十秒差距的垂直气体循环。非定常流出和流入之间的相互作用导致形成具有内部湍流运动的几何厚环面。结果，活动星系核在很宽的立体角范围内被遮蔽。在准稳态下，对于爱丁顿光度为10%和1%的活动星系核，柱密度对<1023 cm−2黑洞的张开角分别约为±30°和±50°。通过环的质量流入与流出和内部湍流运动共存，中心秒差距区域的平均质量吸积速率为2 × 10−4 <$10 −3 M yr−1;这比维持活动星系核亮度所需的吸积速率小10倍。这意味着相对明亮的活动星系核活动本质上是间歇性的，或者有其他机制，如恒星能量反馈，增强了质量吸积到中心。
We propose a plausible mechanism to explain the formation of the so-called obscuring tori around active galactic nuclei (AGNs) based on three-dimensional hydrodynamic simulations including radiative feedback from the central source. The X-ray heating and radiation pressure on the gas are explicitly calculated using a ray-tracing method. This radiation feedback drives a “fountain,” that is, a vertical circulation of gas in the central few to tens parsecs. Interaction between the non-steady outflows and inflows causes the formation of a geometrically thick torus with internal turbulent motion. As a result, the AGN is obscured for a wide range of solid angles. In a quasi-steady state, the opening angles for the column density toward a black hole <1023 cm−2 are approximately ±30° and ±50° for AGNs with 10% and 1% Eddington luminosity, respectively. Mass inflows through the torus coexist with the outflow and internal turbulent motion, and the average mass accretion rate to the central parsec region is 2 × 10−4 ∼ 10−3 M☉ yr−1; this is about 10 times smaller than accretion rate required to maintain the AGN luminosity. This implies that relatively luminous AGN activity is intrinsically intermittent or that there are other mechanisms, such as stellar energy feedback, that enhance the mass accretion to the center.