The Kinematic Bimodality: Efficient Feedback and Cold Gas Deficiency in Slow-rotating Galaxies

Abstract

The bimodality in the stellar spin of low-redshift (massive) galaxies, ubiquitously existing at all star formation levels and in diverse environments, 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 are evidence of a fast quenching history with significant gas outflows. In this work, we measure the spin parameter λ R e , i.e., the normalized specific angular momentum of stars, out of the MaNGA integral field spectroscopy for about 10,000 galaxies. Among the two-thirds with H i follow-up observations ( z ≲ 0.05), we find that, compared to fast-rotating galaxies of the same stellar mass and star formation, the galaxy populations with slower rotation are generally more H i gas-poor, robust against further environmental restriction and with nondetections properly taken into account using the stacking technique. This cold gas deficit of slow-rotating galaxies is most apparent at high mass ∼ 10 11  ⊙ below the star formation main sequence, supporting the pivotal role of gas outflows in their quenching history. With hints from H i 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 disk galaxies the feedback energy mostly goes to the hot circumgalactic medium rather than directly impacting the dense and planar cold gas, thus making the feedback mainly preventive against further gas inflow.