Are High $\Sigma_1$ Massive Blue Spiral Galaxies Rejuvenated Systems?

Abstract

Quiescent galaxies generally possess denser cores than star-forming galaxies with similar mass. As a measurement of the core density, the central stellar mass surface density within a radius of 1 kpc ($\Sigma_1$) was thus suggested to be closely related to galaxy quenching. Massive star-forming galaxies with high $\Sigma_1$ do not fit into this picture. To understand the origin of such galaxies, we compare the spatially-resolved stellar population and star formation properties of massive ($ > 10^{10.5}{\rm M}_{\odot}$) blue spiral galaxies with high and low $\Sigma_1$, divided by $\Sigma_1 = 10^{9.4} M_\odot \, {\rm kpc}^{-2}$, based on the final release of MaNGA IFU data. We find that both high $\Sigma_1$ and low $\Sigma_1$ blue spirals show large diversities in stellar population and star formation properties. Despite the diversities, high $\Sigma_1$ blue spirals are statistically different from the low $\Sigma_1$ ones. Specifically, the radial profiles of the luminosity-weighted age and Mgb/${\rm \langle Fe \rangle}$ show that high $\Sigma_1$ blue spirals consist of a larger fraction of galaxies with younger and less $\alpha$-element enhanced centers than their low $\Sigma_1$ counterparts, $\sim 55\%$ versus $\sim 30\%$. The galaxies with younger centers mostly have higher central specific star formation rates, which still follow the spaxel-based star formation main sequence relation though. Examinations of the H$\alpha$ velocity field and the optical structures suggest that galactic bars or galaxy interactions should be responsible for the rejuvenation of these galaxies. The remaining $\sim 45\% $ of high $\Sigma_1$ blue spirals are consistent with the inside-out growth scenario.