The MASSIVE Survey. XVII. A Triaxial Orbit-based Determination of the Black Hole Mass and Intrinsic Shape of Elliptical Galaxy NGC 2693

Abstract

We present a stellar dynamical mass measurement of a newly detected supermassive black hole (SMBH) at the center of the fast-rotating, massive elliptical galaxy NGC 2693 as part of the MASSIVE survey. We combine high signal-to-noise ratio integral field spectroscopy (IFS) from the Gemini Multi-Object Spectrograph with wide-field data from the Mitchell Spectrograph at McDonald Observatory to extract and model stellar kinematics of NGC 2693 from the central ∼150 pc out to ∼2.5 effective radii. Observations from Hubble Space Telescope WFC3 are used to determine the stellar light distribution. We perform fully triaxial Schwarzschild orbit modeling using the latest TriOS code and a Bayesian search in 6D galaxy model parameter space to determine NGC 2693's SMBH mass ( M _BH ), stellar mass-to-light ratio, dark matter content, and intrinsic shape. We find ${M}_{\mathrm{BH}}=\left(1.7\pm 0.4\right)\times {10}^{9}\ {M}_{\odot }$ and a triaxial intrinsic shape with axis ratios p = b / a = 0.902 ± 0.009 and $q=c/a={0.721}_{-0.010}^{+0.011}$ , triaxiality parameter T = 0.39 ± 0.04. In comparison, the best-fit orbit model in the axisymmetric limit and (cylindrical) Jeans anisotropic model of NGC 2693 prefer ${M}_{\mathrm{BH}}=\left(2.4\pm 0.6\right)\times {10}^{9}\ {M}_{\odot }$ and ${M}_{\mathrm{BH}}=\left(2.9\pm 0.3\right)\times {10}^{9}\ {M}_{\odot }$ , respectively. Neither model can account for the non-axisymmetric stellar velocity features present in the IFS data.

Keywords

• Galaxy dynamics
• Galaxy masses
• Supermassive black holes
• Early-type galaxies
• Galaxies
• Galaxy dark matter halos