The kinematic bimodality: Efficient feedback and cold gas deficiency in slow-rotating galaxies

TL;DR

This study reveals that slow-rotating, spheroid-dominated galaxies exhibit a significant cold gas deficiency and faster quenching, likely due to high-ejectivity feedback-driven outflows, contrasting with fast-rotating disc galaxies.

Contribution

It provides the first large-scale analysis linking stellar spin to cold gas content and feedback mechanisms in low-redshift galaxies.

Findings

Slow-rotating galaxies are more HI gas-poor than fast rotators at similar mass.

Cold gas deficiency is most pronounced at high mass (~10^{11} M_sun) below the star formation main sequence.

High ejective feedback efficiency facilitates massive gas outflows in slow rotators.

Abstract

The bimodality in the stellar spin of low redshift (massive) galaxies, ubiquitously existing at all star formation levels and in diverse environment, suggests that galaxies grow and quench through two diverged evolutionary pathways. For spheroid-dominated galaxies of slow stellar rotation, the age composition and metallicity of their stellar populations evidence a fast quenching history with significant gas outflows. In this work, we measure the spin parameter $\lambda_{R_{\rm e}}$, i.e. the normalized specific angular momentum of stars, out of the MaNGA integral field spectroscopy for about 10000 galaxies. Among the two thirds with HI follow-up observations ($z\lesssim0.05$), we find that, compared to fast-rotating galaxies of the same stellar mass and star formation, the galaxy population of slower rotation are generally more HI gas-poor, robust against further environmental restriction and with non-detections taken into proper account using stacking technique. This cold gas deficit of slow-rotating galaxies is most apparent at high mass $\sim10^{11}\mathcal{M}_{\odot}$ below the star formation main sequence, supporting the pivotal role of gas outflows in their quenching history. With hints from HI velocity distributions, we suspect that massive gas outflows among the slow-rotating population are facilitated by high ejective feedback efficiency, which is a result of extensive coupling between disturbed volume-filling cold gas and (commonly) biconical feedback from central black holes. By contrast, in fast-rotating disc galaxies the feedback energy mostly goes to the hot circumgalactic medium rather than directly impacts the dense and planar cold gas, thus making the feedback mainly preventive against further gas inflow.