Testing the robustness of black hole mass measurements with ALMA and MUSE

We present our ongoing work of using two independent tracers to estimate the supermassive black hole mass in the nearby early-type galaxy NGC 6958; namely integrated stellar and molecular gas kinematics. We used data from the Atacama Large Millimeter/submillimeter Array (ALMA), and the adaptive-optics assisted Multi-Unit Spectroscopic Explorer (MUSE) and constructed state-of-the-art dynamical models. The different methods provide black hole masses of (2.89±2.05)×10⁸M_⊙ from stellar kinematics and (1.35±0.09)×10⁸M_⊙ from molecular gas kinematics which are consistent within their 3σ uncertainties. Compared to recent M_BH - σ_e scaling relations, we derive a slightly over-massive black hole. Our results also confirm previous findings that gas-based methods tend to provide lower black hole masses than stellar-based methods. More black hole mass measurements and an extensive analysis of the method-dependent systematics are needed in the future to understand this noticeable discrepancy.