The James Webb Space Telescope has discovered a surprising population of bright galaxies in the very early Universe (≲500 Myr after the Big Bang) that is hard to explain with conventional galaxy-formation models and whose physical properties are not fully understood. Insight into their internal physics is best captured through nebular lines, but at these early epochs, the brightest of these spectral features are redshifted into the mid-infrared and remain elusive. Using the mid-infrared instrument onboard the James Webb Space Telescope, here we present a detection of Hα and doubly ionized oxygen ([O iii] 4959,5007 Å) from the bright, ultra-high-redshift galaxy candidate GHZ2/GLASS-z12. Based on these emission lines, we infer a spectroscopic redshift of z = 12.33 ± 0.04, placing this galaxy just ~400 Myr after the Big Bang. These observations provide key insights into the conditions of this primaeval, luminous galaxy, which shows hard ionizing conditions rarely seen in the local Universe and probably driven by a compact and young burst (≲30 Myr) of star formation. The galaxy’s oxygen-to-hydrogen abundance is close to a tenth of the solar value, indicating a rapid metal enrichment. This study establishes the unique conditions of this notably bright and distant galaxy and the huge potential of mid-infrared observations to characterize these primordial systems.

詹姆斯·韦伯太空望远镜在非常早期的宇宙中（大爆炸后≲500 Myr）发现了一个令人惊讶的明亮星系群，这很难用传统的星系形成模型来解释，而且其物理特性也不完全清楚。最好通过星云线来了解它们的内部物理学，但在这些早期时期，这些光谱特征中最亮的光谱特征会红移到中红外线，仍然难以捉摸。利用詹姆斯·韦伯太空望远镜（James Webb Space Telescope）上的中红外仪器，我们在这里展示了从明亮的超高红移候选星系GHZ2/GLASS-z12中探测到的Hα和双电离氧（[O iii] 4959,5007 Å）。根据这些发射线，我们推断出 z = 12.33 ± 0.04 的光谱红移，使这个星系在大爆炸后只有 ~400 Myr。这些观测为了解这个原始的发光星系的条件提供了关键见解，它显示了在本地宇宙中很少见的硬电离条件，并且可能是由紧凑而年轻的恒星形成爆发（≲30 Myr）驱动的。该星系的氧到氢的丰度接近太阳值的十分之一，这表明金属富集迅速。这项研究确定了这个非常明亮和遥远的星系的独特条件，以及中红外观测在描述这些原始系统方面的巨大潜力。