美国普林斯顿大学O. Grace Telford团队研究了在极度缺乏金属和尘埃的狮子座P星系中的氢分子。2025年6月11日出版的《自然》杂志发表了这项成果。

詹姆斯·韦伯太空望远镜（JWST）揭示了早期宇宙中出乎意料的快速星系组装，这与星系形成模型相矛盾。在早期星系中，重金属（金属）和尘埃的丰度较低，分子氢的形成及其与恒星形成的关系仍然知之甚少。一些模型预测，恒星主要在低金属丰度的原子气体中形成，而在高金属丰度的分子气体中形成。尽管进行了多次搜索，但在任何低于7%太阳金属量的星系中都没有观测到冷分子气体。 

研究组报告了在3%太阳金属量星系狮子座中唯一一颗O型恒星附近检测到分子氢的旋转发射 P JWST的中红外仪器/中分辨率光谱学（MIRI-MRS）观测模式。这些观察为狮子座设定了一个下限 P的分子气体含量，以及O星照射下的光解区域的建模表明，它是一个紧凑的（半径≤2.6 pc），大约为10⁴ M_⊙云。

研究组还报告了阿塔卡马大型毫米/亚毫米阵列（ALMA）深度搜索对一氧化碳（CO）排放的严格上限。该研究结果强调了MIRI-MRS在低金属性条件下表征即使是小的紫外线照射分子云的能力，在这种情况下，传统的观测示踪剂CO是没有信息的。这一发现将分子气体以可检测量存在的极限金属丰度降低了两倍以上，为早期星系中的星际介质模型提供了至关重要的经验指导。

附：英文原文

Title: Molecular hydrogen in the extremely metal- and dust-poor galaxy Leo P

Author: Telford, O. Grace, Sandstrom, Karin M., McQuinn, Kristen B. W., Glover, Simon C. O., Tarantino, Elizabeth J., Bolatto, Alberto D., Rickards Vaught, Ryan J.

Issue&Volume: 2025-06-11

Abstract: The James Webb Space Telescope (JWST) has revealed unexpectedly rapid galaxy assembly in the early Universe, in tension with galaxy-formation models1,2,3. At the low abundances of heavy elements (metals) and dust typical in early galaxies, the formation of molecular hydrogen and its connection to star formation remain poorly understood. Some models predict that stars form in predominantly atomic gas at low metallicity4,5, in contrast to molecular gas at higher metallicities6. Despite repeated searches7, cold molecular gas has not yet been observed in any galaxy below 7% solar metallicity8. Here we report the detection of rotational emission from molecular hydrogen near the only O-type star in the 3% solar metallicity galaxy LeoP (refs.9,10) with JWST’s Mid-Infrared Instrument/Medium Resolution Spectroscopy (MIRI-MRS) observing mode. These observations place a lower limit on LeoP’s molecular gas content, and modelling of the photodissociation region illuminated by the O star suggests a compact (≤2.6pc radius), approximately 104M⊙ cloud. We also report a stringent upper limit on carbon monoxide (CO) emission from a deep search with the Atacama Large Millimeter/submillimeter Array (ALMA). Our results highlight the power of MIRI-MRS to characterize even small ultraviolet-illuminated molecular clouds in the low-metallicity regime, in which the traditional observational tracer CO is uninformative. This discovery pushes the limiting metallicity at which molecular gas is present in detectable quantities more than a factor of two lower, providing crucial empirical guidance for models of the interstellar medium in early galaxies.

DOI: 10.1038/s41586-025-09115-7

Source: https://www.nature.com/articles/s41586-025-09115-7