Exploring the Origin of Rejuvenating Gas from MaNGA Nearby Galaxies

This study investigates the origin of gas fueling secondary star formation, i.e., rejuvenation in nearby galaxies. From the MaNGA IFU survey, we use stellar absorption features D${}_n$4000 and H${\delta }_A$ to identify regions that started the rejuvenation within the last $\sim$200~Myr. We compare the gas-phase metallicity, metallicity gradients, environments, and H\Romannum{1} gas fractions of the rejuvenating galaxies (RJGs) to controlled star-forming and quiescent galaxy samples. We demonstrate that, for the majority of RJGs, the rejuvenating gas is originally in the galaxy rather than accreted gas. The evidence includes: (1) gas metallicities consistent with the mass-metallicity relation of SF galaxies; (2) metallicity gradients that are not flattened, arguing against radial inflows; (3) gas velocities in rejuvenating regions consistent with their surroundings, and (4) high H\Romannum{1} gas fractions comparable to SF galaxies, indicating a pre-existing reservoir. Furthermore, we find no evidence that the rejuvenating events are triggered by tidal interactions with neighbors. While internal processes appear to dominate, we also present a clear example of rejuvenation triggered by gas accretion. The galaxy MaNGA 12080-12705 hosts a low-metallicity, kinematically distinct star-forming region in an overall old, massive galaxy, providing unambiguous evidence of an external origin, such as accretion or a minor merger. Our analysis demonstrates that using D${}_n$4000 and EW(H${\delta }_A$) provides a reliable way to identify current rejuvenation events in large spectroscopic surveys. The method will enable statistical studies to understand rejuvenation across cosmic time.