The 36 GHz Class I Methanol Maser in NGC 4945: A Tracer of Active Galactic Nucleus-driven Outflow–Interstellar Medium Interaction

Abstract Extragalactic Class I methanol masers are well-established tracers of bar-driven shocks in several nearby galaxies, but whether active galactic nucleus (AGN)-driven outflows can also excite such masers has remained unclear. We present high-angular-resolution interferometric observations of the 36.2 GHz Class I methanol maser in the Seyfert 2 galaxy NGC 4945 using the Australia Telescope Compact Array and complementary Atacama Large Millimeter/submillimeter Array data of molecular gas and shock tracers, which provide the first unambiguous case of Class I masers associated with a large-scale AGN-driven outflow. The maser emission is resolved into three complexes (A, B, C) that exhibit a striking spatial and kinematic alignment with the AGN-driven bipolar molecular outflow. These masers coincide with local peaks of gas excitation (high CO line ratio R 32 ∼ 3) and velocity dispersion ( σ v > 30 km s −1 ). A clear chemical dichotomy is revealed: masers strongly correlate with SiO, a tracer of outflow shocks, but are spatially offset from HNCO features linked to bar-driven inflow. Multiepoch observations over ∼7 yr show significant variability of methanol masers, consistent with evolving shock conditions. Our study establishes that AGN-driven outflows are capable of producing Class I methanol masers, demonstrating their utility as a unique shock-specific diagnostic for probing AGN feedback in galactic nuclei.