Department of Astronomy, University of Massachusetts, Amherst, MA, USA.
Cosmic Dawn Center (DAWN), Copenhagen, Denmark.
Nature. 2021 Sep;597(7877):485-488. doi: 10.1038/s41586-021-03806-7. Epub 2021 Sep 22.
Star formation in half of massive galaxies was quenched by the time the Universe was 3 billion years old. Very low amounts of molecular gas seem to be responsible for this, at least in some cases, although morphological gas stabilization, shock heating or activity associated with accretion onto a central supermassive black hole are invoked in other cases. Recent studies of quenching by gas depletion have been based on upper limits that are insufficiently sensitive to determine this robustly, or stacked emission with its problems of averaging. Here we report 1.3 mm 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 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.
到宇宙形成 30 亿年时，一半的大质量星系中的恒星形成已经被熄灭。至少在某些情况下，非常少量的分子气体似乎对此负责，尽管在其他情况下，形态气体稳定、激震加热或与中心超大质量黑洞吸积相关的活动被援引为原因。最近对气体消耗引起的熄灭的研究基于灵敏度不足的上限，不足以可靠地确定这一点，或者是堆积发射及其平均化问题。在这里，我们报告了对 6 个强烈透镜星系尘埃发射的 1.3 毫米观测结果，这些星系中的恒星形成已经被熄灭，放大倍数高达 30 倍。在尘埃发射中，有四个星系没有被探测到，尘埃质量的估计上限为恒星质量的 0.0001 倍，通过代理（假设银河系的分子气体与尘埃的比例）为恒星质量的 0.01 倍。这是在类似红移的恒星形成星系中每单位恒星质量的分子气体少了两个数量级。从这些小样本中进行外推仍然很困难，但这些观测结果表明，在一些高红移星系中，气体消耗是恒星形成停止的原因。
