2026-06-16 千葉大学
図:ビッグバンから約7億年後の宇宙に存在する銀河A1689-zD1（背景）、とアルマ望遠鏡による観測から検出された中性酸素からの輝線（等高線およびスペクトル）
＜関連情報＞
- https://www.chiba-u.ac.jp/news/research-collab/post_688.html
- https://iopscience.iop.org/article/10.3847/1538-4357/ae5bad
ALMAによるz ∼ 7の星形成銀河からの[O I ] 145 μmおよび[N II ] 205 μm輝線観測 ALMA Observations of [O i] 145 μm and [N ii] 205 μm Emission Lines from Star-forming Galaxies at z ∼ 7
Yoshinobu Fudamoto, Akio K. Inoue, Rychard Bouwens, Hanae Inami, Renske Smit, Daniel P. Stark, Manuel Aravena, Andrea Pallottini, Takuya Hashimoto, Masamune Oguri,…
The Astrophysical Journal Published: 2026 June 15
DOI:10.3847/1538-4357/ae5bad
Abstract
We present results of new observations of [O i] 145 μm and [N ii] 205 μm emission lines from four star-forming galaxies at redshifts between z = 6.58 and 7.68 that have previous detections of [C ii] 158 μm and dust continua. Using the Atacama Large Millimeter/submillimeter Array, we successfully detect [O i] 145 μm emission from all targets at >4σ significance. However, [N ii] 205 μm emission is undetected in all galaxies (signal-to-noise ratio < 3.5σ) except for a tentative detection from A1689-zD1. From the observed high [C ii]/[N ii] emission line ratios (≳20−80), we find that most of the [C ii] 158 μm emission arises from neutral gas regions (3σ lower limits of ≳74%−96%). From [O i] 145 μm, [C ii] 158 μm lines, and IR luminosities, we estimate the neutral gas densities of nH = 103.5–106 cm−3 and the far-UV (FUV) radiation strengths of G0 ∼ 102.5–103. While the neutral gas densities are similar to those of high-redshift starburst galaxies, the FUV strengths are lower compared to both local and high-redshift starbursts. Finally, we estimate atomic hydrogen masses using [O i] 145 μm emission lines and the oxygen abundances measured from recent JWST observations. We find gas mass ratios of fgas ∼ 0.3–0.8, which are similar to earlier studies using [C ii] 158 μm. Starting from this pilot observation, future large [O i] 145 μm emission line surveys will provide us with currently little-known neutral gas properties of star-forming galaxies in the early Universe.
