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

Katherine E Whitaker,Keren Sharon,Mohammad Akhshik,Pieter G Van Dokkum,Desika Narayanan,Camilla Pacifici,Erica J Nelson,Sune Toft,Gabriel B Brammer,Justin S Spilker,Lamiya Mowla,Georgios E Magdis,Rachel Bezanson,Christina C Williams,Francesco Valentino,Joel Leja,Johan Richard,Allison Man,Alexandra Pope

doi:10.1038/s41586-021-03806-7

Abstract

Star formation in half of massive galaxies was quenched by the time the Universe was 3 billion years old1. Very low amounts of molecular gas seem to be responsible for this, at least in some cases2-7, although morphological gas stabilization, shock heating or activity associated with accretion onto a central supermassive black hole are invoked in other cases8-11. Recent studies of quenching by gas depletion have been based on upper limits that are insufficiently sensitive to determine this robustly2-7, or stacked emission with its problems of averaging8,9. Here we report 1.3mm observations of dust emission from 6 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 redshifts12-14. 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.

Highlights

Star formation in half of massive galaxies was quenched by the time the Universe was three billion years old[1]
The 1.3mm observations were made with the Atacama Large Millimeter/submillimeter Array (ALMA) and the sample comprises of six galaxies selected from the REsolving QUIEscent Magnified (REQUIEM) galaxy survey: MRG-M134115, MRG-M013816, MRG-M212917, MRG-M015016, MRG-M045418, and MRG-M142318 (Figure 1)
While the most distant target, MRG-M1423, has a more typical star-formation rate of ~140 M⊙yr-1 over the previous 100 Myr, consistent with normal star-forming galaxies at z = 3, its spectrum reveals classic post-starburst signatures that support a picture where it has quenched rapidly within the last 100 Myr 18. These targets are qualitatively different than existing millimeter/carbon monoxide (CO) data tracing cold interstellar medium phases in quenched galaxies in that they have order of magnitude lower star-formation rates for their stellar mass[2,4,5,6,8,11], higher redshifts[3,7,9,10], and uniquely deep flux limits facilitated by strong lensing magnification

Summary

Introduction

Star formation in half of massive galaxies was quenched by the time the Universe was three billion years old[1]. These targets are qualitatively different than existing millimeter/carbon monoxide (CO) data tracing cold interstellar medium phases in quenched galaxies in that they have order of magnitude lower star-formation rates for their stellar mass[2,4,5,6,8,11], higher redshifts[3,7,9,10], and uniquely deep flux limits facilitated by strong lensing magnification.

Results

Conclusion