国立天文台科学研究部

2023.11.10 highlights

Rapid Increase in Oxygen in Early Universe 

Using extensive observational data from the James Webb Space Telescope, a research team led by a Project Assistant Professor Kimihiko Nakajima of the National Astronomical Observatory of Japan has examined the oxygen abundance (*) in the early Universe. Their findings show a remarkable increase in oxygen abundance in galaxies during the first 500-700 million years after the birth of the Universe.  

Visit the following links for more information. 

ICRR, Univ. Tokyo:  

 [English]  https://www.icrr.u-tokyo.ac.jp/en/news/14330/

 [Japanese] https://www.icrr.u-tokyo.ac.jp/news/14329/

NAOJ: 

 [English] https://www.nao.ac.jp/en/news/science/2023/20231110-dos.html 

 [Japanese] https://www.nao.ac.jp/news/science/2023/20231110-dos.html 

The results are published in the Astrophysical Journal Supplement Series on November 13, 2023 under the title “JWST Census for the Mass-Metallicity Star Formation Relations at z = 4-10 with Self-consistent Flux Calibration and Proper Metallicity Calibrators.” 

Authors: Kimihiko Nakajima, Masami Ouchi, Yuki Isobe, Yuichi Harikane, Yechi Zhang, Yoshiaki Ono, Hiroya Umeda, and Masamune Oguri 

DOI: 10.3847/1538-4365/acd556 

URL: https://iopscience.iop.org/article/10.3847/1538-4365/acd556 

(*) Oxygen abundance refers to the ratio of the number of oxygen (O) to that of hydrogen (H), denoted as (O/H). Hydrogen, being an element present since the birth of the universe, is used as the reference. 

Figure 1: A compilation of two-dimensional infrared spectra from 138 galaxies in the universe dating back to 12.2 to 13.3 billion years ago, obtained by the research team through the analysis of observations made with the James Webb Space Telescope’s near-infrared spectrograph NIRSpec. The spectra are ordered by increasing redshift (decreasing universe age) from bottom to top. The inset window displays an example, depicting an image and one-dimensional spectrum of a single galaxy. Highlighted areas show emission lines from elements like hydrogen and oxygen. The cosmic expansion causes these lines to shift to longer wavelengths (towards the right). By analyzing the intensity of these lines, scientists can determine elemental abundances, including oxygen. 
(Illustration credit: NASA, ESA, CSA, K. Nakajima et al.)  
Figure 2: Infrared images (taken with JWST/NIRCam) of six galaxies from 500-700 million years after the birth of the Universe. All 6 show a deficit in the oxygen abundance. Such deficiency is not commonly observed on average in galaxies from the present up to 13.1 billion years ago, underscoring a rapid increase in oxygen abundance within galaxies during the first 500-700 million years of the Universe. 
(Illustration credit: NASA, ESA, CSA, K. Nakajima et al.)