Identifying and distinguishing quenching galaxies with spatially resolved star formation in TNG50

TL;DR

This study uses the TNG50 simulation to develop observationally motivated metrics based on spatial star formation distribution, effectively distinguishing between different quenching galaxy types and their evolutionary stages.

Contribution

The paper introduces new morphological metrics derived from simulations to identify and differentiate inside-out and outside-in quenching galaxies in large surveys.

Findings

Metrics can separate quenched from star-forming galaxies based on morphology.

Inside-out quenched galaxies are often the most massive in their halos.

Outside-in quenched galaxies are typically satellites in dense environments.

Abstract

Using the TNG50 simulation, we determine observationally motivated metrics that can distinguish quenching galaxies from star forming galaxies for $M_{*} \geqslant 10^{9.5}~M_{\odot}$, based on the spatial distribution of their stellar populations. Quenching galaxies are not fully quenched but have low levels of ongoing star formation that decreases over time. The morphological metrics consider the concentration of star formation, size of the star forming disk, and characteristic radii that trace sharp truncations of star formation. These metrics can separate simulated quenching galaxies based on morphology into populations where star formation is suppressed inside-out and outside-in. Inside-out quenched galaxies are more likely to be the most massive galaxy within their halo in the field, while outside-in quenched galaxies are satellites residing in dense environments and begin quenching ${\sim} 1~\text{Gyr}$ after being accreted. Outside-in quenched galaxies typically take ${\sim} 1.5~\text{Gyr}$ to quench, and inside-out quenched galaxies can take up to ${\sim} 3.5~\text{Gyr}$, where the duration of quenching is a function of stellar mass. We find that each population of quenched galaxy experiences evolution of their morphological metrics, where the different quenched populations reside in unique locations in parameter space. Galaxies in the later stages of quenching are more easily distinguished than those in the early stages, when compared to star forming galaxies. In addition, inside-out quenched galaxies can be distinguished compared to outside-in quenched galaxies, and the progress through the quenching episode can be estimated for both populations. These results have broad implications for distinguishing quenching galaxies in large galaxy surveys.