The Diverse Molecular Gas Content of Massive Galaxies Undergoing Quenching at z~1

TL;DR

This study investigates the molecular gas content and quenching processes in three massive galaxies at z~1, revealing diverse evolutionary stages and highlighting the importance of measurement methods in understanding galaxy quenching.

Contribution

It provides new insights into the molecular gas fractions, star formation histories, and quenching mechanisms of massive galaxies at z~1, emphasizing the impact of different SFR measurement techniques.

Findings

Molecular gas fractions are 13-23% in the studied galaxies.

Depletion times vary significantly depending on SFR measurement method.

Recently quenched and star-forming galaxies have similar depletion times when using spectral fitting.

Abstract

We present a detailed study of the molecular gas content and stellar population properties of three massive galaxies at 1 < z < 1.3 that are in different stages of quenching. The galaxies were selected to have a quiescent optical/near-infrared spectral energy distribution and a relatively bright emission at 24 micron, and show remarkably diverse properties. CO emission from each of the three galaxies is detected in deep NOEMA observations, allowing us to derive molecular gas fractions Mgas/Mstar of 13-23%. We also reconstruct the star formation histories by fitting models to the observed photometry and optical spectroscopy, finding evidence for recent rejuvenation in one object, slow quenching in another, and rapid quenching in the third system. To better constrain the quenching mechanism we explore the depletion times for our sample and other similar samples at z~0.7 from the literature. We find that the depletion times are highly dependent on the method adopted to measure the star formation rate: using the UV+IR luminosity we obtain depletion times about 6 times shorter than those derived using dust-corrected [OII] emission. When adopting the star formation rates from spectral fitting, which are arguably more robust, we find that recently quenched galaxies and star-forming galaxies have similar depletion times, while older quiescent systems have longer depletion times. These results offer new, important constraints for physical models of galaxy quenching.