Cross-checking SMBH mass estimates in NGC 6958-I. Stellar dynamics from adaptive optics-Assisted MUSE observations

Abstract

Supermassive black hole masses ( M BH ) can dynamically be estimated with various methods and using different kinematic tracers. Different methods have only been cross-checked for a small number of galaxies and often show discrepancies. To understand these discrepancies, detailed cross-comparisons of additional galaxies are needed. We present the first part of our cross-comparison between stellar-And gas-based M BH estimates in the nearby fast-rotating early-Type galaxy NGC 6958. The measurements presented here are based on ground-layer adaptive optics-Assisted Multi-Unit Spectroscopic Explorer (MUSE) science verification data at around 0 . 6 spatial resolution. The spatial resolution is a key ingredient for the measurement and we provide a Gaussian parametrization of the adaptive optics-Assisted point spread function for various wavelengths. From the MUSE data, we extracted the stellar kinematics and constructed dynamical models. Using an axisymmetric Schwarzschild technique, we measured an M BH of (3 . 6 + 2 . 7-2 . 4 ) × 10 8 M at 3 significance taking kinematical and dynamical systematics (e.g. radially varying mass-To-light ratio) into account. We also added a dark halo, but our data do not allow us to constrain the dark matter fraction. Adding dark matter with an abundance matching prior results in a 25 per cent more massive black hole. Jeans anisotropic models return M BH of (4 . 6 + 2 . 5-2 . 7 ) × 10 8 and (8 . 6 + 0 . 8-0 . 8 ) × 10 8 M at 3 confidence for spherical and cylindrical alignments of the velocity ellipsoid, respectively. In a follow-up study, we will compare the stellar-based M BH with those from cold and warm gas tracers, which will provide additional constraints for the M BH for NGC 6958, and insights into assumptions that lead to potential systematic uncertainty.