2026ApJ...999..263L

Statistically, green valley (GV) galaxies exhibit lower molecular gas fractions (f_gas) and reduced star formation efficiency (SFE) compared to star-forming galaxies. However, it remains unclear whether quenching is primarily driven by one factor or results from a combination of mechanisms in individual GV galaxies. In this study, we address this question by examining the spatial distributions of star formation and molecular gas in 28 GVs selected from the ALMaQUEST survey and additional literature samples. For each galaxy, we identify regions with suppressed specific star formation rate (sSFR) and measure Δf_gas and ΔSFE-offsets from the resolved scaling relations of the star-forming main-sequence galaxies. By comparing the fraction of regions with negative Δf_gas and ΔSFE, we classify 35.7% ± 13.2% (57.1% ± 17.9%) of GV galaxies as f_gas driven, 39.3% ± 14.0% (39.3% ± 14.0%) as SFE driven, and 25.0% ± 10.6% (3.6% ± 3.6%) as mixed mode when adopting a fixed (variable) CO-to-H₂ conversion factor (α_CO). These results indicate that GVs undergo quenching through multiple pathways. As sSFR decreases from the main sequence to the GV, we observe a transition toward predominantly SFE-driven quenching, possibly linked to internal processes such as morphological quenching or active galactic nucleus activity. We further estimate the quenching timescale (τ_decay), defined as the time from the peak star formation rate to 1 e^–1 (approximately 37%) of its value, using integrated MaNGA spectra. SFE-driven quenching is typically associated with short τ_decay, while f_gas-driven quenching shows a broader range. Overall, 75% of GVs exhibit τ_decay shorter than 1 Gyr, suggesting that quenching in most GVs proceeds rapidly, challenging purely slow-quenching scenarios like starvation.