Extragalactic water megamasers are beacons of accretion onto supermassive black holes. At 22 GHz, water megamaser emission is a powerful tool to map accurate nuclear accretion disks, yield estimates of the enclosed mass, and determine accurate distances to the parent galaxies. In this talk, I will summarize the work carried out on water megamaser emission over the last 20 years, in both nearby and higher redshift galaxies. The advent of ALMA, for the first time, has opened up the opportunity to explore the rich sub-millimeter water spectrum which will help reveal new structures and complex dynamics.  I will present here some of the first results obtained with ALMA at 183, 321 and 325 GHz, and highlight the unique role that ALMA plays in resolving those locations. The study of these sub-millimeter lines probes regions in which longer wavelength maser emission at 22 GHz is subject to obscuration, mapping out the physical conditions of the gas around active nuclei, and placing important constraints on the still unclear, complex excitation mechanism for water.

Water megamaser emission in galaxies

2019 Fall National Meeting

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