High-frequency water megamasers as precision probes of black holes, galaxies and cosmology: A case for a next-generation sub-mm/mm interferometer
Abstract
Water megamasers in the circumnuclear disks of active galactic nuclei are among the most precise probes of supermassive black holes. VLBI imaging of 22 GHz disk masers has provided geometric distances to independently constrain H0, accurate black hole mass measurements, and sub-parsec views of accretion disk geometry. ALMA has opened a new window into water maser transitions in the sub-mm/mm regime, which trace temperatures, densities and disk regions that are inaccessible at 22 GHz, and can be observed at higher spatial resolution and with less free-free absorption. However, current detections are limited to a few bright extragalactic masers in nearby galaxies. We present the case for a next-generation sub-mm/mm interferometer - ALMA2040 - that would open a new parameter space for maser studies. We show that a 10-fold increase in line sensitivity and three times longer baselines compared to ALMA would transform sub-mm maser studies from a few bright detections into a population-level probe, delivering black hole masses and geometric distances from sub-mm masers alone, independent of and complementary to 22 GHz measurements. Integrated into a VLBI array, ALMA2040 would resolve maser disks out to >160 Mpc, extend maser black hole masses into the largely untested intermediate-mass regime, reveal magnetic field structure in accretion disks through polarization studies, and test systematics in H0 measurements.
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BibTeX
@misc{zaw2026highfrequency,
title = {{High-frequency water megamasers as precision probes of black holes, galaxies and cosmology: A case for a next-generation sub-mm/mm interferometer}},
author = {Ingyin Zaw and C. M. Violette Impellizzeri and Dominic W. Pesce and Elizabeth Humphreys and Hannah R. Stacey and Sophie Venselaar and Chengyu Kuo and Jack Gallimore and Yoshiaki Hagiwara and Satoki Matsushita and Jim Braatz},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.22239},
eprint = {2610.22239},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.22239},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - High-frequency water megamasers as precision probes of black holes, galaxies and cosmology: A case for a next-generation sub-mm/mm interferometer
AU - Ingyin Zaw
AU - C. M. Violette Impellizzeri
AU - Dominic W. Pesce
AU - Elizabeth Humphreys
AU - Hannah R. Stacey
AU - Sophie Venselaar
AU - Chengyu Kuo
AU - Jack Gallimore
AU - Yoshiaki Hagiwara
AU - Satoki Matsushita
AU - Jim Braatz
PY - 2026
DA - 2026/10/15
PB - arXiv
DO - 10.48550/arxiv.2610.22239
UR - https://arxiv.org/abs/2610.22239
AB - Water megamasers in the circumnuclear disks of active galactic nuclei are among the most precise probes of supermassive black holes. VLBI imaging of 22 GHz disk masers has provided geometric distances to independently constrain H_0, accurate black hole mass measurements, and sub-parsec views of accretion disk geometry. ALMA has opened a new window into water maser transitions in the sub-mm/mm regime, which trace temperatures, densities and disk regions that are inaccessible at 22 GHz, and can be observed at higher spatial resolution and with less free-free absorption. However, current detections are limited to a few bright extragalactic masers in nearby galaxies. We present the case for a next-generation sub-mm/mm interferometer - ALMA2040 - that would open a new parameter space for maser studies. We show that a 10-fold increase in line sensitivity and three times longer baselines compared to ALMA would transform sub-mm maser studies from a few bright detections into a population-level probe, delivering black hole masses and geometric distances from sub-mm masers alone, independent of and complementary to 22 GHz measurements. Integrated into a VLBI array, ALMA2040 would resolve maser disks out to >160 Mpc, extend maser black hole masses into the largely untested intermediate-mass regime, reveal magnetic field structure in accretion disks through polarization studies, and test systematics in H_0 measurements.
ER -