The physical connection between central stellar surface density and stellar spin in SAMI and MaNGA nearby galaxies

TL;DR

This study investigates the link between central stellar surface density and stellar spin in nearby galaxies, revealing that their correlation varies with star formation activity and galaxy evolution stage.

Contribution

It provides new empirical evidence connecting central density and stellar kinematics, highlighting how this relationship differs between star-forming and passive galaxies.

Findings

Correlation between $ m \Sigma_{1}$ and $ m \lambda_{re}$ in star-forming galaxies

Passive galaxies show a wider range of stellar spin at fixed $ m \Sigma_{1}$

Passive galaxies are more structurally heterogeneous than star-forming ones.

Abstract

The stellar surface density within the inner 1 kpc ($\Sigma_{1}$) has become a popular tool for understanding the growth of galaxies and its connection with the quenching of star formation. The emerging picture suggests that building a central dense core is a necessary condition for quenching. However, it is not clear whether changes in $\Sigma_{1}$ trace changes in stellar kinematics and the growth of dispersion-dominated bulges. In this paper, we combine imaging from the Sloan Digital Sky Survey with stellar kinematics from the Sydney-AAO Multi-object Integral-field unit (SAMI) and Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) surveys to quantify the correlation between $\Sigma_{1}$ and the proxy for stellar spin parameter within one effective radius ($\lambda_{re}$) for 1599 nearby galaxies. We show that, on the star-forming main sequence and at fixed stellar mass, changes in $\Sigma_{1}$ are mirrored by changes in $\lambda_{re}$. While forming stars, main sequence galaxies remain rotationally-dominated systems, with their $\Sigma_{1}$ increasing but their stellar spin staying either constant or slightly increasing. The picture changes below the main sequence, where $\Sigma_{1}$ and $\lambda_{re}$ are no longer correlated. Passive systems show a narrower range of $\Sigma_{1}$, but a wider range of $\lambda_{re}$ compared to star-forming galaxies. Our results indicate that, from a structural point of view, passive galaxies are a more heterogeneous population than star-forming systems, and may have followed a variety of evolutionary paths. This also suggests that, if dispersion-dominated bulges still grow significantly at $z\sim$0, this generally takes place during, or after, the quenching phase.