Are High-Σ1 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 (Σ _1 ) was thus suggested to be closely related to galaxy quenching. Massive star-forming galaxies with high Σ _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 M _⊙ ) blue spiral galaxies with high and low Σ _1 , divided by Σ _1 = 10 ^9.4 M _⊙ kpc ^−2 , based on the final release of MaNGA integral field unit data. We find that both high-Σ _1 and low-Σ _1 blue spirals show large diversities in stellar population and star formation properties. Despite the diversities, high-Σ _1 blue spirals are statistically different from the low-Σ _1 ones. Specifically, the radial profiles of the luminosity-weighted age and Mgb/〈Fe〉 show that high-Σ _1 blue spirals consist of a larger fraction of galaxies with younger and less α -element-enhanced centers than their low-Σ _1 counterparts, ∼55% versus ∼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. Examinations of the H α velocity field and the optical structures suggest that galactic bars or galaxy interactions should be responsible for the rejuvenation of these galaxies. The remaining ∼45% of high-Σ _1 blue spirals are consistent with the inside-out growth scenario.

Keywords

• Galaxy evolution
• Galaxy formation
• Galaxy ages
• Spiral galaxies
• Galaxy spectroscopy