M87の3D画像:銀河の中心部にあるブラックホールの質量を特定するための新たな見解が示される(M87 in 3D: New view of galaxy helps pin down mass of the black hole at its core)


2023-04-13 カリフォルニア大学バークレー校(UCB)



M87のケック望遠鏡による積分視野分光で、三軸銀河とブラックホール質量が判明 Keck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Galaxy and a Revised Black Hole Mass

Emily R. Liepold, Chung-Pei Ma, and Jonelle L. Walsh
The Astrophysical Journal Letters  Published 2023 March 15

Figure 1.


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 $({5.37}_{-0.25}^{+0.37}\pm 0.22)\times {10}^{9}{M}_{\odot }$, where the second error indicates the systematic uncertainty associated with the distance to M87.