M87的Keck积分场光谱观测揭示其本质三轴椭球结构与修正的黑洞质量
Keck Integral-Field Spectroscopy of M87 Reveals an Intrinsically Triaxial Galaxy and a Revised Black Hole Mass
AI总结：
基于Keck II望远镜的积分场光谱观测，本文通过三轴Schwarzschild轨道建模揭示了M87星系具有强三轴结构，并修正了其中心黑洞质量。
摘要：
星系的三维本征形状和中心超大质量黑洞的质量，为理解宇宙时间内星系的成长历史提供了关键洞察。假设星系为球形或轴对称形状的标准做法可能过于简化，并会使由星系内恒星运动推断出的黑洞质量产生偏差。本文基于Keck II望远镜的积分场光谱观测，给出了M87在二维 $250\mbox{$^{\prime\prime}$} \times 300\mbox{$^{\prime\prime}$}$ 连续视场内的空间分辨恒星运动学，覆盖了50 pc至12 kpc的径向范围。从约5 kpc向外，我们探测到显著的25 $\mathrm{km~s}^{-1}$ 旋转模式，其中运动学轴（连接最大远离速度与接近速度的轴线）与M87的光度主轴存在 $40^\circ$ 的错位。在内部5 kpc区域内，旋转幅度和错位角度均有所减小。这种错位且扭曲的速度场是三轴结构的典型特征，表明M87并非轴对称形状的星系。采用包含超过4000个观测约束的三轴Schwarzschild轨道建模，使我们能够同时确定其形状和质量参数。这些模型纳入了由恒星族群研究提出的恒星质光比径向递减分布。我们发现M87具有强三轴性，其中长轴与中轴之比 $p=0.845$，短轴与长轴之比 $q=0.722$，并确定其黑洞质量为 $(5.37^{+0.37}_{-0.25}\pm 0.22)\times 10^9 M_\odot$，其中第二个误差项表示与M87距离相关的系统不确定性。
英文摘要：
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 $250\mbox{$^{\prime\prime}$} \times 300\mbox{$^{\prime\prime}$}$ 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 $\mathrm{km~s}^{-1}$ rotational pattern, in which the kinematic axis (connecting the maximal receding and approaching velocities) is $40^\circ$ 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 $(5.37^{+0.37}_{-0.25}\pm 0.22)\times 10^9 M_\odot$, where the second error indicates the systematic uncertainty associated with the distance to M87.
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