The masses of the supermassive black holes found in galaxy bulges are correlated with a multitude of galaxy properties1,2, leading to suggestions that galaxies and black holes may evolve together3. The number of reliably measured black-hole masses is small, and the number of methods for measuring them is limited4, holding back attempts to understand this co-evolution. Directly measuring black-hole masses is currently possible with stellar kinematics (in early-type galaxies), ionized-gas kinematics (in some spiral and early-type galaxies5,6,7) and in rare objects that have central maser emission8. 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 NGC 4526, and obtain a best fit that requires the presence of a central dark object of × 108 solar masses (3σ confidence limit). With the next-generation millimetre-wavelength interferometers these observations could be reproduced in galaxies out to 75 megaparsecs in less than 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 are accessible with current techniques.
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The research leading to these results has received funding from the European Community’s Seventh Framework Programme. M.B. is supported by the rolling grants ‘Astrophysics at Oxford’ and from the UK Research Councils. M.C. acknowledges support from a Royal Society University Research Fellowship. M.S. acknowledges support from a Science and Technology Facilities Council Advanced Fellowship. Support for the construction of CARMA was derived from the states of California, Illinois and Maryland, the James S. McDonnell Foundation, the Gordon and Betty Moore Foundation, the Kenneth T. and Eileen L. Norris Foundation, the University of Chicago, the Associates of the California Institute of Technology, and the National Science Foundation. Ongoing development and operations of CARMA are supported by the National Science Foundation under a cooperative agreement, and by the CARMA partner universities.
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Astronomy & Astrophysics (2019)