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arXiv 1502.07767astro-ph.GAastro-ph.CO
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用光谱天体测量法空间分辨<100 μas类星体宽线区的动能

Spatially Resolving the Kinematics of the <100 μas Quasar Broad Line Region using Spectroastrometry

Jonathan Stern, Joseph F. Hennawi, Jörg-Uwe Pott

摘要:

亮活动星系核(AGN)的宽线区(BLR)是超大质量黑洞吸积流的一个重要观测特征,它可以用来测量宇宙历史中超大质量黑洞的质量(M_BH)。由于BLR的角尺寸<100 μas,目前对BLR运动学的直接约束仅限于混响映射研究提供的约束,这些研究在低光度L和低红移z AGN上进行最有效。我们分析了测量BLR大小的可能性,并使用光谱天体测量研究其运动学结构,从而测量发射线光子的空间位置质心作为速度的函数。我们计算预期的光谱信号的旋转占主导地位的BLR的各种假设的比率的随机旋转运动,和径向分布的BLR气体。我们发现对于z < 2.5的超亮类星体,低电离BLR的大小已经可以用现有的望远镜和自适应光学系统来限制,从而提供了一种新的方法来空间解析10^3 - 10^4引力半径的吸积流的运动学,并测量AGN族高L端的M_BH。使用30米级的望远镜,BLR光谱天文学应该可以常规地探测到z ~ 6的更暗的类星体和各种发射线。这将使运动学M_BH测量成为光度和红移的函数,为下一代望远镜提供了令人信服的科学案例。

英文摘要:

The broad line region (BLR) of luminous active galactic nuclei (AGN) is a prominent observational signature of the accretion flow around supermassive black holes, which can be used to measure their masses (M_BH) over cosmic history. Due to the <100 μas angular size of the BLR, current direct constraints on BLR kinematics are limited to those provided by reverberation mapping studies, which are most efficiently carried out on low-luminosity L and low-redshift z AGN. We analyze the possibility to measure the BLR size and study its kinematic structure using spectroastrometry, whereby one measures the spatial position centroid of emission line photons as a function of velocity. We calculate the expected spectroastrometric signal of a rotation-dominated BLR for various assumptions about the ratio of random to rotational motions, and the radial distribution of the BLR gas. We show that for hyper-luminous quasars at z < 2.5, the size of the low-ionization BLR can already be constrained with existing telescopes and adaptive optics systems, thus providing a novel method to spatially resolve the kinematics of the accretion flow at 10^3 -- 10^4 gravitational radii, and measure M_BH at the high-L end of the AGN family. With a 30m-class telescope, BLR spectroastrometry should be routinely detectable for much fainter quasars out to z ~ 6, and for various emission lines. This will enable kinematic M_BH measurements as a function of luminosity and redshift, providing a compelling science case for next generation telescopes.

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