Exploring the Origin of Rejuvenating Gas from MaNGA Nearby Galaxies

Abstract

This study investigates the origin of secondary star formation, i.e., rejuvenation in nearby galaxies. From the MaNGA IFU survey, we use stellar absorption features, D${}_n$4000 and EW(H${\delta }_{\mathrm{A}}$), to identify regions that started the rejuvenation within the last $\sim$200~Myr and use gas-phase metallicity as a primary tracer for accretion of pristine gas, in order to verify the mechanism that triggers the rejuvenation. We compare the metallicity and the velocity of rejuvenating regions with typical star-forming regions. We also compare metallicity gradients, environments, \ion{H}{1} gas fractions, and visual morphologies of galaxies hosting rejuvenating regions to controlled star-forming and quiescent galaxy samples. Overall, we do not find the rejuvenating regions or their hosts show anomalies in metallicity, kinematics, and visual morphology to the controlled comparison samples. These observations suggest that local rejuvenation is likely fueled by gas already residing within the host rather than accreted from outside, and reflect the short life time of small scale dense gas clouds. On the contrary, if the rejuvenation is fueled by gas accretion, the chemical and mixing timescale should be much shorter than $\sim 100$ Myr so that no chemical and kinematical anomalies are measured. Meanwhile, we report a clear case of a massive quiescent galaxy brought back to star-forming by accreting gas. Our method of identifying rejuvenation is simple and effective, and can be applied to large spectroscopic surveys to investigate the origin of rejuvenation across cosmic time.

Accepted for publication in ApJ. DOI: https://doi.org/10.3847/1538-4357/ae9093