On the Origin of Quenched but Gas-rich Regions at Kiloparsec Scales in Nearby Galaxies

TL;DR

This study investigates the origins of gas-rich but quenched regions in nearby galaxies, revealing that local properties like stellar surface density are key to quenching, independent of global galaxy characteristics.

Contribution

It introduces a new classification of quenched regions based on resolved spectroscopy and employs machine learning to identify local factors driving star formation cessation.

Findings

Gas-rich quenched regions are common in high-mass, red, non-AGN galaxies.

Stellar surface density is the most important predictor for quenching.

Low-mass hot evolved stars likely support gas against gravitational collapse.

Abstract

We use resolved spectroscopy from MaNGA to investigate the significance of both local and global properties of galaxies to the cessation of star formation at kpc scales. Quenched regions are identified from a sample of isolated disk galaxies by a single-parameter criterion $\rm {D}_n(4000)$ - $\log$ $\rm {EW}({H\alpha})$$~>1.6-\log 2=1.3$, and are divided into gas-rich quenched regions (GRQRs) and gas-poor quenched regions (GPQRs) according to the surface density of cold gas ($\rm \Sigma_{gas}$). Both types of quenched regions tend to be hosted by non-AGN galaxies with relatively high mass ($M_\ast$$\gtrsim 10^{10}M_\odot$) and red colors (${\rm NUV}-r \gtrsim 3$), as well as low star formation rate and high central density at fixed mass. They span wide ranges in other properties including structural parameters that are similar to the parent sample, indicating that the conditions responsible for quenching in gas-rich regions are largely independent on the global properties of galaxies. We train random forest (RF) classifiers and regressors for predicting quenching in our sample with 15 local/global properties. $\Sigma_\ast$ is the most important property for quenching, especially for GRQRs. These results strongly indicate the important roles of low-mass hot evolved stars which are numerous and long-lived in quenched regions and can provide substantial radiation pressure to support the surrounding gas against gravitational collapse. The different feature importance for quenching as found previously by Bluck et al. (2020a,b) are partly due to the different definitions of quenched regions, particularly the different requirements on $\rm {EW}({H\alpha})$.