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

TL;DR

This study compares supermassive black hole mass estimates in galaxy NGC 6958 using stellar and molecular gas kinematics, highlighting method-dependent discrepancies and the need for further systematic analysis.

Contribution

It demonstrates the use of ALMA and MUSE data with advanced dynamical models to measure black hole masses via two independent tracers in a single galaxy.

Findings

Stellar kinematics estimate: (2.89±2.05)×10^8 M☉

Gas kinematics estimate: (1.35±0.09)×10^8 M☉

Gas-based methods tend to give lower black hole masses

Abstract

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 $(2.89\pm 2.05) \times 10^8M_{\odot}$ from stellar kinematics and $(1.35\pm 0.09) \times 10^8M_{\odot}$ from molecular gas kinematics which are consistent within their $3\sigma$ uncertainties. Compared to recent M$_{\rm BH}$ - $\sigma_{\rm e}$ 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.