Galactic Rain: Inflowing Cool Gas in Red Geyser Galaxies and Their Connection to Radio Activity and Interactions

Dead galaxies with low star formation rates dominate the local universe, yet the processes that quench and maintain their quiescence remain uncertain. One candidate is energy released by the supermassive black hole at the center of galaxies – active galactic nuclei (AGN) – which can expel or heat gas and suppress star formation. A recently identified population of galaxies known as "red geysers" offers a key window into this phenomenon. These galaxies are no longer forming stars and show presence of weak but large-scale, biconical ionized gas outflows, possibly driven by low-luminosity AGNs. Here, we study the kinematics of the Na I D absorption, which traces the cool (T ~ 100–1000 K) neutral gas phase and can serve as a fuel for both star formation and AGN activity in the future. Using a sample of 140 red geysers from the Sloan Digital Sky Survey-IV Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, we characterize spatially resolved velocity centroids and linewidths for every red geyser galaxy and find that the majority of the cool gas is inflowing with median velocities of ~ 88 km/s. The absorption features are also dynamically cold, with linewidths approximately 0.46 times those of the stellar component, indicating coherent motion. We further investigate the connection between cool gas inflows, radio activity, and galaxy environment. Red geysers with radio detections and those with morphological signatures of interaction both tend to exhibit stronger inflowing Na I D absorption. We conclude that galaxy interactions represent a fertile channel for replenishing cool gas in red geysers, sustaining accretion and radio emission, and revealing that quiescent systems are governed by cycles of inflow, feedback, and regulation.