Triaxial Orbit-Modeled 22-Billion-Solar-Mass Black Hole in Holmberg 15A
Spatially resolved Keck KCWI stellar kinematics of the brightest cluster galaxy Holmberg 15A reveal a photometric/kinematic axis misalignment that betrays a triaxial 3D shape. Triaxial Schwarzschild orbit-superposition modeling of ~2500 kinematic constraints yields a black-hole mass of ~2.16x10^10 solar masses, among the most massive known locally and well above the M_BH-sigma relation. Imposing axisymmetry degrades the fit and biases the mass high, demonstrating that triaxial dynamical modeling is required for accurate SMBH masses in cored massive ellipticals.
Draft version January 6, 2025 Typeset using LATEX twocolumn style in AASTeX631 A 22-Billion Solar
Using Keck KCWI integral-field spectroscopy over a ~100x100 arcsec field, the authors obtain spatially resolved stellar kinematics of Holmberg 15A (H15A), the very low-surface-brightness brightest cl…