I. Physikalisches Institut, Universität zu Köln, Köln, Germany.
Max-Planck-Institut für Radioastronomie, Bonn, Germany.
Nature. 2022 Feb;602(7895):58-62. doi: 10.1038/s41586-021-04294-5. Epub 2022 Feb 2.
Distortions of the observed cosmic microwave background provide a direct measurement of the microwave background temperature at redshifts from 0 to 1 (refs. ). Some additional background temperature estimates exist at redshifts from 1.8 to 3.3 based on molecular and atomic line-excitation temperatures in quasar absorption-line systems, but are model dependent. No deviations from the expected (1 + z) scaling behaviour of the microwave background temperature have been seen, but the measurements have not extended deeply into the matter-dominated era of the Universe at redshifts z > 3.3. Here we report observations of submillimetre line absorption from the water molecule against the cosmic microwave background at z = 6.34 in a massive starburst galaxy, corresponding to a lookback time of 12.8 billion years (ref. ). Radiative pumping of the upper level of the ground-state ortho-HO(1-1) line due to starburst activity in the dusty galaxy HFLS3 results in a cooling to below the redshifted microwave background temperature, after the transition is initially excited by the microwave background. This implies a microwave background temperature of 16.4-30.2 K (1σ range) at z = 6.34, which is consistent with a background temperature increase with redshift as expected from the standard ΛCDM cosmology.
观测到的宇宙微波背景的扭曲提供了对红移从 0 到 1（参考文献）的微波背景温度的直接测量。基于类星体吸收线系统中的分子和原子谱线激发温度，在红移从 1.8 到 3.3 处存在一些额外的背景温度估计，但这些估计取决于模型。尚未观察到微波背景温度与预期的（1+z）标度行为的偏差，但这些测量尚未深入到红移 z>3.3 的宇宙物质主导时代。在这里，我们报告了在一个大质量星暴星系中观测到的水分子对宇宙微波背景的亚毫米线吸收，对应于回溯时间为 128 亿年（参考文献）。尘埃星系 HFLS3 中的星暴活动导致基态正 HO(1-1)线的上能级因辐射抽运而冷却到低于红移微波背景温度，最初通过微波背景激发跃迁。这意味着在 z=6.34 处微波背景温度为 16.4-30.2K（1σ 范围），与标准ΛCDM 宇宙学所预期的随红移增加的背景温度增加一致。
