Gas and stellar kinematic misalignment in MaNGA galaxies: What is the origin of counter-rotating gas?

Context. Kinematic misalignment between gas and stellar components is observed in a certain fraction of galaxies. It believed to be caused by the acquisition of gas from the external reservoir by, for example, major or minor mergers, accretion from cosmological filaments, or the circumgalactic medium.Aims. We aim to constrain the possible sources of the gas that forms the counter-rotating component.Methods. We derived the gas-phase oxygen abundances of 69 galaxies with a kinematic misalignment between gas and stellar components from the MaNGA DR17 survey and compared them with the metallicity expected according to the mass-metallicity relation.Results. We find that the oxygen abundance of the counter-rotating gas in our sample is higher than 8.2 dex, which rules out a significant role for the inflow of pristine gas. Meanwhile, there is a significant difference in the oxygen abundance of the counter-rotating gas between red and blue galaxies. In general, the oxygen abundance is lower than expected for the stellar mass in red galaxies but is compatible with or even higher than typical values for the stellar mass in blue galaxies.Conclusions. We show that the exchange of enriched gas between galaxies is the most plausible mechanism for explaining the metallicity of counter-rotating gas components in galaxies of all masses and colors. Meanwhile, minor mergers may play a significant role in the formation of counter-rotating gas components in red and quenched galaxies.

Automated summary

Kinematic misalignment between gas and stellar components in galaxies is caused by the acquisition of gas from external reservoirs, and the exchange of enriched gas between galaxies is the most plausible mechanism for explaining the metallicity of counter-rotating gas components. The oxygen abundance of the counter-rotating gas is higher than expected for pristine gas, and there is a significant difference in the oxygen abundance between red and blue galaxies. Minor mergers may play a significant role in the formation of counter-rotating gas components in red and quenched galaxies.