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arXiv 1603.04523astro-ph.GA
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用ALMA研究黑洞质量:NGC 1332作为分子盘动力学的一个例子

Toward Precision Black Hole Masses with ALMA: NGC 1332 as a Case Study in Molecular Disk Dynamics

A. J. Barth, J. Darling, A. J. Baker, B. D. Boizelle, D. A. Buote, L. C. Ho, J. L. Walsh

摘要:

我们提出的第一个结果,从阿塔卡马大型毫米/亚毫米阵列(ALMA)CO(2-1)的早期型星系的环核气体盘的观测计划。该计划的目的是探测中心黑洞引力影响范围内的气体。在NGC 1332中,0.3”分辨率的ALMA数据揭示了来自高度倾斜(i~ 83度)的环核盘的CO发射,在空间上与哈勃太空望远镜图像中看到的尘埃盘一致。该盘显示出中心向上翻转的最大视线速度达到+-500公里/秒相对于系统速度,与预期的签名的快速旋转周围的超大质量黑洞。旋转展宽和光束拖尾在光盘中心附近产生复杂和不对称的线轮廓。我们构建了动力学模型的旋转磁盘和拟合模型的CO线轮廓直接ALMA数据立方体。内部圆盘中旋转和湍流速度色散之间的简并性排除了对黑洞质量的强约束的推导,但是模型拟合允许湍流色散幅度的合理范围意味着中心质量在~(4-8)x10^8 Msun的范围内。我们认为,气体运动观测解决的黑洞的投影半径的影响沿磁盘的短轴将有能力产生黑洞质量测量,在很大程度上是不敏感的湍流或恒星质量分布的系统不确定性。对于高度倾斜的圆盘,这是一个比通常的影响范围准则更为严格的要求。

英文摘要:

We present first results from a program of Atacama Large Millimeter/submillimeter Array (ALMA) CO(2-1) observations of circumnuclear gas disks in early-type galaxies. The program was designed with the goal of detecting gas within the gravitational sphere of influence of the central black holes. In NGC 1332, the 0.3"-resolution ALMA data reveal CO emission from the highly inclined (i~ 83 degrees) circumnuclear disk, spatially coincident with the dust disk seen in Hubble Space Telescope images. The disk exhibits a central upturn in maximum line-of-sight velocity reaching +-500 km/s relative to the systemic velocity, consistent with the expected signature of rapid rotation around a supermassive black hole. Rotational broadening and beam smearing produce complex and asymmetric line profiles near the disk center. We constructed dynamical models for the rotating disk and fitted the modeled CO line profiles directly to the ALMA data cube. Degeneracy between rotation and turbulent velocity dispersion in the inner disk precludes the derivation of strong constraints on the black hole mass, but model fits allowing for a plausible range in the magnitude of the turbulent dispersion imply a central mass in the range ~(4-8)x10^8 Msun. We argue that gas-kinematic observations resolving the black hole's projected radius of influence along the disk's minor axis will have the capability to yield black hole mass measurements that are largely insensitive to systematic uncertainties in turbulence or in the stellar mass profile. For highly inclined disks, this is a much more stringent requirement than the usual sphere-of-influence criterion.

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