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 integral field spectroscopy (IFS) from the Gemini Multi-Object Spectrograph (GMOS) with wide-field data from the Mitchell Spectrograph at McDonald Observatory to extract and model stellar kinematics of NGC 2693 from the central $\sim 150$ pc out to $\sim 2.5$ effective radii. Observations from Hubble Space Telescope (HST) 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 6-D galaxy model parameter space to determine NGC 2693's SMBH mass ($M_{\text{BH}}$), stellar mass-to-light ratio, dark matter content, and intrinsic shape. We find $M_{\text{BH}}=\left(1.7\pm 0.4\right)\times 10^9{M}_{\odot }$ and a triaxial intrinsic shape with axis ratios $p=b/a=0.902\pm 0.009$ and $q=c/a=0.721_{-0.010}^{+0.011}$, triaxiality parameter $T=0.39\pm 0.04$. In comparison, the best-fit orbit model in the axisymmetric limit and (cylindrical) Jeans anisotropic model of NGC 2693 prefer $M_{\text{BH}}=\left(2.4\pm 0.6\right)\times 10^9{M}_{\odot }$ and $M_{\text{BH}}=\left(2.9\pm 0.3\right)\times 10^9{M}_{\odot }$, respectively. Neither model can account for the non-axisymmetric stellar velocity features present in the IFS data.

18 pages, 9 figures, 2 tables, accepted to ApJ 2022/02/24

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