Quenching, Mergers and Age Profiles for z=2 Galaxies in IllustrisTNG

TL;DR

This study uses IllustrisTNG simulations to analyze young quiescent galaxies at z=2, revealing diverse age profiles and the roles of mergers and starbursts in galaxy quenching and structural evolution.

Contribution

It demonstrates that mergers significantly influence galaxy quenching and structure, but alternative pathways also exist, providing new insights into galaxy evolution at high redshift.

Findings

Over half of the simulated young quiescent galaxies show positive age gradients.

Recent intense central starbursts are often triggered by significant mergers.

A notable fraction of recently quenched galaxies lack major mergers and have flat age profiles.

Abstract

Using the IllustrisTNG cosmological galaxy formation simulations, we analyze the physical properties of young quiescent galaxies at z=2 with stellar masses above 10^10.5 solar masses. This key population provides an unaltered probe into the evolution of galaxies from star-forming to quiescent and has been recently targeted by several observational studies. Young quiescent galaxies in the simulations do not appear unusually compact, in tension with observations, but they show unique age gradients that are qualitatively consistent with the observed color gradients. In particular, more than half of the simulated young quiescent galaxies show positive age profiles due to recent intense central starbursts, which are triggered by significant mergers. Yet, there is a sizable population of recently quenched galaxies without significant mergers and with flat age profiles. Our results suggest that mergers play a fundamental role in structural transformation, but are not the only available pathway to quench a z=2 galaxy.