A black-hole mass measurement from molecular gas kinematics in NGC4526

TL;DR

This paper demonstrates that modeling molecular gas kinematics from CO emission allows accurate measurement of supermassive black-hole masses, expanding the potential for such measurements in many galaxies beyond current methods.

Contribution

It introduces a new method using molecular gas kinematics to measure black-hole masses, applicable with future interferometers like ALMA.

Findings

Measured black-hole mass in NGC4526 as approximately 4.5x10^8 solar masses.

Method can be applied to galaxies up to 75 Mpc away with next-generation telescopes.

Potential to increase the number of black-hole mass measurements significantly.

Abstract

The masses of the supermassive black-holes found in galaxy bulges are correlated with a multitude of galaxy properties, leading to suggestions that galaxies and black-holes may evolve together. The number of reliably measured black-hole masses is small, and the number of methods for measuring them is limited, holding back attempts to understand this co-evolution. Directly measuring black-hole masses is currently possible with stellar kinematics (in early-type galaxies), ionised-gas kinematics (in some spiral and early-type galaxies) and in rare objects which have central maser emission. Here we report that by modelling the effect of a black-hole on the kinematics of molecular gas it is possible to fit interferometric observations of CO emission and thereby accurately estimate black hole masses. We study the dynamics of the gas in the early-type galaxy NGC4526, and obtain a best fit which requires the presence of a central dark-object of 4.5(+4.2-3.0)x10^8 Msun (3 sigma confidence limit). With next generation mm-interferometers (e.g. ALMA) these observations could be reproduced in galaxies out to 75 megaparsecs in less the 5 hours of observing time. The use of molecular gas as a kinematic tracer should thus allow one to estimate black-hole masses in hundreds of galaxies in the local universe, many more than accessible with current techniques.