ALMA Observations of [OI]145um and [NII]205um Emission lines from Star-Forming Galaxies at $z\sim7$

Yoshinobu Fudamoto; Akio K. Inoue; Rychard Bouwens; Hanae Inami; Renske Smit; Dan Stark; Manuel Aravena; Andrea Pallottini; Takuya Hashimoto; Masamune Oguri; Rebecca A. A. Bowler; Elisabete da Cunha; Pratika Dayal; Andrea Ferrara; Seiji Fujimoto; Kasper E. Heintz; Alexander P. S. Hygate; Ivana F. van Leeuwen; Ilse De Looze; Lucie E. Rowland; Mauro Stefanon; Yuma Sugahara; Joris Witstok; Paul P. van der Werf

arXiv · 2504.03831

ALMA Observations of [OI]145um and [NII]205um Emission lines from Star-Forming Galaxies at $z\sim7$

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Abstract

We present results of new observations of [OI]145um and [NII]205um emission lines from four star-forming galaxies at redshifts between $z=6.58$ and $7.68$ that have previous detections of \Ciium\ and dust continua. Using ALMA, we successfully detect [OI]145um emission from all targets at $>4\,σ$ significance. However, [NII]205um emission is undetected in all galaxies (SNR $<3.5\,σ$) except for a tentative detection from A1689-zD1. From the observed high [CII]/[NII] emission line ratios ($\gtrsim20 - 80$), we find that most of the [CII]158um emission arise from neutral gas regions ($3\,σ$ lower limits of $\gtrsim 74 - 96\%$). From [OI]145um, [CII]158um lines, and infrared luminosities, we estimate the neutral gas densities of $n_{\rm H}=10^{3.5}$ - $10^6\,{\rm cm^{-3}}$ and the far-ultraviolet (FUV) radiation strengths of $G_0\sim10^{2.5}$-$10^{3}$. 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 [OI]145um emission lines and the oxygen abundances measured from recent JWST observations. We find gas mass ratios of $f_{\rm gas}\sim0.3$ - $0.8$, which are similar to earlier studies using [CII]158um. Starting from this pilot observation, future large [OI]145um emission line surveys will provide us with currently little-known neutral gas properties of star-forming galaxies in the early Universe.

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Yoshinobu Fudamoto, Akio K. Inoue, Rychard Bouwens, Hanae Inami, Renske Smit, Dan Stark, Manuel Aravena, Andrea Pallottini, Takuya Hashimoto, Masamune Oguri, Rebecca A. A. Bowler, Elisabete da Cunha, Pratika Dayal, Andrea Ferrara, Seiji Fujimoto, Kasper E. Heintz, Alexander P. S. Hygate, Ivana F. van Leeuwen, Ilse De Looze, Lucie E. Rowland, Mauro Stefanon, Yuma Sugahara, Joris Witstok, Paul P. van der Werf. 2025-04-04. ALMA Observations of [OI]145um and [NII]205um Emission lines from Star-Forming Galaxies at $z\sim7$. https://arxiv.org/abs/2504.03831

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