Keck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Galaxy and a Revised Black Hole Mass
Keck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Galaxy and a Revised Black Hole Mass
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DOI：
10.3847/2041-8213/acbbcf
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发表时间：
2023-02
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影响因子：
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通讯作者：
Emily R. Liepold;Chung-Pei Ma;J. Walsh
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作者：
Emily R. Liepold;Chung-Pei Ma;J. Walsh
星系的三维固有形状和中心超大质量黑洞的质量为了解星系在宇宙时间内的成长历史提供了关键信息。球形或轴对称形状的标准假设可能过于简单，并且可能会使从星系内恒星运动推断的黑洞质量产生偏差。在这里，我们提出了空间分辨恒星运动学的M87在一个二维的250″ × 300″连续的领域，覆盖径向范围为50 pc-12 kpc的积分场光谱观测凯克II望远镜。从大约5 kpc向外，我们探测到一个显著的25 km s−1的旋转模式，其中运动学轴（连接最大的后退和接近速度）与M87的光度主轴偏离40°。在5 kpc以内，旋转振幅和失准角均减小.这种错位和扭曲的速度场是三轴性的标志，表明M87不是一个轴对称形状的星系。三轴史瓦西轨道建模超过4000个观测约束，使我们能够同时确定的形状和质量参数。该模型纳入了径向下降的恒星质量-光比的恒星人口研究建议的配置文件。我们发现M87是强三轴的，中长主轴的比率p = 0.845，短长主轴的比率q = 0.722，并确定黑洞质量为（5.37−0.25+0.37±0.22）× 109 M，其中第二个误差表示与M87距离相关的系统不确定性。
The three-dimensional intrinsic shape of a galaxy and the mass of the central supermassive black hole provide key insight into the galaxy’s growth history over cosmic time. Standard assumptions of a spherical or axisymmetric shape can be simplistic and can bias the black hole mass inferred from the motions of stars within a galaxy. Here, we present spatially resolved stellar kinematics of M87 over a two-dimensional 250″ × 300″ contiguous field covering a radial range of 50 pc–12 kpc from integral-field spectroscopic observations at the Keck II Telescope. From about 5 kpc and outward, we detect a prominent 25 km s−1 rotational pattern, in which the kinematic axis (connecting the maximal receding and approaching velocities) is 40° misaligned with the photometric major axis of M87. The rotational amplitude and misalignment angle both decrease in the inner 5 kpc. Such misaligned and twisted velocity fields are a hallmark of triaxiality, indicating that M87 is not an axisymmetrically shaped galaxy. Triaxial Schwarzschild orbit modeling with more than 4000 observational constraints enabled us to determine simultaneously the shape and mass parameters. The models incorporate a radially declining profile for the stellar mass-to-light ratio suggested by stellar population studies. We find that M87 is strongly triaxial, with ratios of p = 0.845 for the middle-to-long principal axes and q = 0.722 for the short-to-long principal axes, and determine the black hole mass to be (5.37−0.25+0.37±0.22)×109M⊙ , where the second error indicates the systematic uncertainty associated with the distance to M87.