Quenching of star formation from a lack of inflowing gas to galaxies

TL;DR

This study provides direct evidence that gas depletion causes star formation quenching in some high-redshift galaxies, using sensitive dust emission observations of strongly lensed galaxies.

Contribution

First direct measurements of dust and molecular gas in quenched high-redshift galaxies using 1.3mm observations of gravitationally lensed systems.

Findings

Four out of six galaxies show no detectable dust emission.

Estimated molecular gas mass is two orders of magnitude lower than in star-forming galaxies.

Gas depletion is confirmed as a mechanism for star formation cessation in some high-redshift galaxies.

Abstract

Star formation in half of massive galaxies was quenched by the time the Universe was three billion years old. Very low amounts of molecular gas appear responsible for this, at least in some cases, though morphological gas stabilization, shock heating, or activity associated with accretion onto a central supermassive black hole is invoked in other cases. Recent studies of quenching by gas depletion have been based upon upper limits that are insufficiently sensitive to determine this robustly, or stacked emission with its problems of averaging. Here we report 1.3mm observations of dust emission from six strongly lensed galaxies where star formation has been quenched, with magnifications of up to a factor of 30. Four of the six galaxies are undetected in dust emission, with an estimated upper limit on the dust mass of 0.0001 times the stellar mass, and by proxy (assuming a Milky Way molecular gas-to-dust ratio) 0.01 times the stellar mass in molecular gas. This is two orders of magnitude less molecular gas per unit stellar mass than seen in star forming galaxies at similar redshifts. It remains difficult to extrapolate from these small samples, but these observations establish that gas depletion is responsible for a cessation of star formation in some fraction of high-redshift galaxies.