WISDOM Project – XIX. Figures of merit for supermassive black hole mass measurements using molecular gas and/or megamaser kinematics

• DOI: 10.1093/mnras/stae1106
• Publication Date: 2024-04-23T20:54:54Z
• Authors: Hengyue Zhang; Martin Bureau; Mark D Smith; Michele Cappellari; Timothy A Davis; Pandora Dominiak; Jacob S Elford; Fu-Heng Liang; Ilaria Ruffa; Thomas G Williams
• Keywords: Megamaser; Black hole (networking)

The mass ($M_\mathrm{BH}$) of a supermassive black hole (SMBH) can be measured using spatially-resolved kinematics the region where SMBH dominates gravitationally. most reliable measurements are those that resolve smallest physical scales around SMBHs. We consider here three metrics to compare probed by kinematic tracers dominated rotation: radius innermost detected tracer $R_\mathrm{min}$ normalised respectively SMBH's Schwarzschild ($R_\mathrm{Schw}\equiv 2GM_\mathrm{BH}/c^2$, $G$ is gravitational constant and $c$ speed light), sphere-of-influence (SOI) ($R_\mathrm{SOI}\equiv GM_\mathrm{BH}/\sigma_\mathrm{e}^2$, $\sigma_\mathrm{e}$ stellar velocity dispersion within galaxy's effective radius) equality [the $R_\mathrm{eq}$ at which equals enclosed mass, $M_\mathrm{BH}=M_*(R_\mathrm{eq})$, $M_*(R)$ $R$]. All lead analogous simple relations between highest circular $V_\mathrm{c}$. Adopting these molecular gas megamaser kinematics, we demonstrate best material physically closer SMBHs in terms $R_\mathrm{Schw}$ but slightly farther $R_\mathrm{SOI}$ $R_\mathrm{eq}$. However, observations nearby galaxies extended configurations Atacama Large Millimeter/sub-millimeter Array SOI comparably well thus enable as precise measurements.