《自然》（20231026出版）一周论文导读

 
 
《自然》（20231026出版）一周论文导读  
 

 

编译 | 冯维维

Nature, Volume 622 Issue 7984, 26 October 2023

《自然》第622卷，7984期，2023年10月26日

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天体物理学Astrophysics

Confirmation and refutation of very luminous galaxies in the early Universe

韦布望远镜观测到早期宇宙明亮星系

▲ 作者：Pablo Arrabal Haro, Mark Dickinson, Steven L. Finkelstein, Jeyhan S. Kartaltepe, Callum T. Donnan, Denis Burgarella, Jorge A. Zavala, etc.

▲ 链接：

https://www.nature.com/articles/s41586-023-06521-7

▲ 摘要：

在宇宙历史的最初5亿年里，第一批恒星和星系形成，给宇宙播下了重元素，并最终重新电离了星系间介质。詹姆斯·韦布太空望远镜观测发现了令人惊讶的大量早期恒星形成星系候选者，根据多波段光度法估计，其距离（红移，z）大到z≈16，远超JWST之前的限制。

虽然这样的光度红移通常是稳健的，但它们可能遭受简并和偶尔的灾难性错误。需要光谱测量来验证这些来源，并可靠地量化可以约束星系形成模型和宇宙学的物理特性。

研究者展示了韦布光谱，证实了两个非常明亮的星系的红移为z>11，并证明了另一个候选星系的红移为z≈16，而非此前认为的z = 4.9，它们具有不寻常的星云线发射和尘埃变红的组合，与更遥远天体的颜色类似。

这些结果加强了早期快速形成非常明亮星系的证据，同时也强调了光谱验证的必要性。大量明亮的早期星系或表明当前星系形成模型的缺陷，或与通常认为在后期成立的物理性质（如恒星初始质量函数）的偏差。

▲ Abstract：

During the first 500 million years of cosmic history, the first stars and galaxies formed, seeding the Universe with heavy elements and eventually reionizing the intergalactic medium Observations with the James Webb Space Telescope (JWST) have uncovered a surprisingly high abundance of candidates for early star-forming galaxies, with distances (redshifts, z), estimated from multiband photometry, as large as z?≈?16, far beyond pre-JWST limits. Although such photometric redshifts are generally robust, they can suffer from degeneracies and occasionally catastrophic errors. Spectroscopic measurements are required to validate these sources and to reliably quantify physical properties that can constrain galaxy formation models and cosmology. Here we present JWST spectroscopy that confirms redshifts for two very luminous galaxies with z > 11, and also demonstrates that another candidate with suggested z ≈ 16 instead has z = 4.9, with an unusual combination of nebular line emission and dust reddening that mimics the colours expected for much more distant objects. These results reinforce evidence for the early, rapid formation of remarkably luminous galaxies while also highlighting the necessity of spectroscopic verification. The large abundance of bright, early galaxies may indicate shortcomings in current galaxy formation models or deviations from physical properties (such as the stellar initial mass function) that are generally believed to hold at later times.

Geophysical evidence for an enriched molten silicate layer above Mars’s core

火核外层存在丰富熔融硅酸盐层

▲ 作者：Henri Samuel, Mélanie Drilleau, Attilio Rivoldini, Zongbo Xu, Quancheng Huang, Rapha?l F. Garcia, Vedran Leki?, Jessica C. E. Irving, James Badro, Philippe H. Lognonné, James A. D. Connolly, Taichi Kawamura, Tamara Gudkova & William B. Banerdt

▲ 链接：

https://www.nature.com/articles/s41586-023-06601-8

▲ 摘要：

在火星上探测到的深反射S波推断出火核的大小为1830±40km，但这需要的轻元素含量与实验岩石学的限制不相容。

一种假设是火星地幔的成分是均匀的，这与最近测量到的沿核心-地幔边界衍射的异常缓慢传播的P波不一致。

另一种假设是，火星的地幔是不均匀的，这是早期岩浆海洋凝固形成一个富含铁和产热元素的基底层的结果。这种富集导致在岩心上方形成熔融硅酸盐层，由部分熔融层覆盖。