2020MNRAS.498.1609K

We present very long baseline interferometry (VLBI) images and kinematics of water maser emission in three active galaxies: NGC 5728, Mrk 1, and IRAS 08452-0011. IRAS 08452-0011, at a distance of ∼200 Mpc, is a triple-peaked H₂O megamaser, consistent with a Keplerian rotating disc, indicating a black hole mass of (3.3±0.2)×10⁷ M_☉. NGC 5728 and Mrk 1 display double-peaked spectra, and VLBI imaging reveals complicated gas kinematics that do not allow for a robust determination of black hole mass. We show evidence that the masers in NGC 5728 are in a wind while the Mrk 1 maser system has both disc and outflow components. We also find that disturbed morphology and kinematics are a ubiquitous feature of all double-peaked maser systems, implying that these maser sources may reside in environments where active galactic nucleus (AGN) winds are prominent at ∼1 pc scale and have significant impact on the masing gas. Such AGNs tend to have black hole masses M_ BH_ < 8 x 10⁶ M_☉ and Eddington ratios λ_ Edd_ ≳0.1, while the triple-peaked megamasers show an opposite trend.