ALMA Observations of [Oi] 145 μm and [Nii] 205 μm Emission Lines from Star-forming Galaxies at z ∼ 7

Fudamoto, Y, Inoue, AK, Bouwens, R, Inami, H, Smit, R ORCID: 0000-0001-8034-7802, Stark, DP, Aravena, M, Pallottini, A, Hashimoto, T, Oguri, M, Algera, H, Bowler, RAA, da Cunha, E, Dayal, P, Ferrara, A, Fujimoto, S, Heintz, KE, Hygate, APS, van Leeuwen, IF, De Looze, I et al (2026) ALMA Observations of [Oi] 145 μm and [Nii] 205 μm Emission Lines from Star-forming Galaxies at z ∼ 7. The Astrophysical Journal, 1004 (2). ISSN 0004-637X

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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.

Item Type:	Article
Uncontrolled Keywords:	5109 Space Sciences; 5101 Astronomical Sciences; 51 Physical Sciences; 5101 Astronomical Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics; 0306 Physical Chemistry (incl. Structural); Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	IOP Publishing
Date of acceptance:	4 April 2026
Date of first compliant Open Access:	16 September 2026
Date Deposited:	16 Sep 2026 07:50
Last Modified:	16 Sep 2026 07:50
DOI or ID number:	10.3847/1538-4357/ae5bad
URI:	https://researchonline.ljmu.ac.uk/id/eprint/29439

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