MASCOT: molecular gas depletion times and metallicity gradients - evidence for feedback in quenching active galaxies

We present results from the first public data release of the MaNGA-ARO Surv e y of CO Targets (MASCOT), focusing our study on galaxies whose star formation rates and stellar masses place them below the ridge of the star-forming main sequence. In optically selected type 2 AGN/low-ionization nuclear emission regions (LINERs)/Composites, we find an empirical relation between gas-phase metallicity gradients & nabla;Z and global molecular gas depletion times t(dep) = M-H2 / SFR with more quenched' systems sho wing flatter/positi ve gradients. Our results are based on the O3N2 metallicity diagnostic (applied to star-forming regions within a given galaxy), which was recently suggested to also be robust against emission by diffuse ionized gas (DIG) and LINERs. We conduct a systematic investigation into possible drivers of the observed & nabla;Z - t(dep) relation (ouflows, gas accretion, in situ star formation, mergers, and morphology). We find a strong relation between & nabla;Z or t(dep) and centralized outflow strength traced by the [O III ] velocity broadening. We also find signatures of suppressed star formation in the outskirts in AGN-like galaxies with long depletion times and an enhancement of metals in the outer regions. We find no evidence of inflows impacting the metallicity gradients, and none of our results are found to be significantly affected by merger activity or morphology. We thus conclude that the observed & nabla;Z-t(dep) relation may stem from a combination of metal redistribution via weak feedback, and a connection to in situ star formation via a resolved relation.

Automated summary

This study presents the first public data release of the MASCOT survey, which focuses on galaxies below the star-forming main sequence. The results show an empirical relation between gas-phase metallicity gradients and global molecular gas depletion times. The study investigates potential drivers of this relation and finds a strong connection to centralized outflow strength and suppressed star formation in the outskirts of AGN-like galaxies. Overall, the observed relation is suggested to be the result of metal redistribution via weak feedback and a connection to in situ star formation.