Galactic Rain: Cool Gas Inflows in Red Geyser Galaxies and Their Connection to AGN Activity and Interactions

TL;DR

This study reveals that red geyser galaxies predominantly host inflowing cool gas, which is linked to AGN activity and environmental interactions, suggesting a cycle of gas inflow, feedback, and quiescence regulation.

Contribution

It provides the first detailed analysis of cool gas inflows in red geysers and their connection to AGN activity and galaxy environment.

Findings

~70% of cool gas in red geysers is inflowing with median velocity ~47 km/s.

Radio-detected red geysers have ~7 times larger inflowing gas reservoirs.

Galactic interactions significantly increase cool gas inflows, fueling AGN activity.

Abstract

Red geysers are a population of massive (log[M/M$_\odot$]~10.5), quiescent galaxies that exhibit large-scale but weak, bi-symmetric ionized gas outflows, interpreted as signatures of ongoing, low-level active galactic nucleus (AGN) feedback. We investigate the kinematics and prevalence of cool (T~100-1000K), neutral gas traced by Na I D absorption, and its connection to galaxy environment and AGN activity. Using 140 red geyser galaxies from the Sloan Digital Sky Survey-IV Mapping Nearby Galaxies at Apache Point Observatory (MaNGA), we measure spatially resolved velocities and dispersions via double-Gaussian fits to the Na I D doublet. We find that ~70% of the cool gas is inflowing, with a median velocity of ~47 km/s (~10% of the expected free-fall speed), and also exhibits kinematically ordered motions with ${\sigma}_{NaD}$/${\sigma_*}$~0.4. Additionally, the Na I D absorption is more prevalent in red geysers than in a matched control sample, showing a higher detection fraction (63% vs 40%) and reservoir areas ~1.6 times larger. Acceleration (~1 Myr) and accretion (~20 Myr) timescales indicate that the absorbing clouds are likely young and short-lived. Another intriguing result is that radio-detected red geysers (30% of the sample) show inflowing gas reservoirs ~7 times larger than in non-radio systems. Similarly, galaxies subject to environmental effects host inflowing gas reservoirs ~2.7 times larger than isolated red geysers. We take this as evidence that galaxy interactions play a key role in replenishing the cool gas reservoirs of red geysers, fueling central AGN activity, sustaining radio emission, and regulating long-term quiescence. These findings reveal that quiescent systems are governed by cycles of inflow, feedback, and regulation.