REBELS-IFU: on the origin of the elevated [OIII]/[CII] ratios in the early Universe
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| Format: | Preprint |
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2025
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| author | Algera, Hiddo Rowland, Lucie Smit, Renske Fisher, Rebecca Ramambason, Lise Kumari, Nimisha Vallini, Livia Inami, Hanae Nanayakkara, Themiya Stefanon, Mauro Aravena, Manuel Bakx, Tom Bouwens, Rychard Bowler, Rebecca Cescon, Karin Chen, Chian-Chou Dayal, Pratika De Looze, Ilse Ferrara, Andrea Fudamoto, Yoshinobu Komarova, Lena van Leeuwen, Ivana Ormerod, Katherine Schouws, Sander Sommovigo, Laura Vijayan, Aswin Wang, Wei-Hao van der Werf, Paul Witstok, Joris |
| author_facet | Algera, Hiddo Rowland, Lucie Smit, Renske Fisher, Rebecca Ramambason, Lise Kumari, Nimisha Vallini, Livia Inami, Hanae Nanayakkara, Themiya Stefanon, Mauro Aravena, Manuel Bakx, Tom Bouwens, Rychard Bowler, Rebecca Cescon, Karin Chen, Chian-Chou Dayal, Pratika De Looze, Ilse Ferrara, Andrea Fudamoto, Yoshinobu Komarova, Lena van Leeuwen, Ivana Ormerod, Katherine Schouws, Sander Sommovigo, Laura Vijayan, Aswin Wang, Wei-Hao van der Werf, Paul Witstok, Joris |
| contents | We present new ALMA [OIII]$_{88}$ observations of eight previously [CII]$_{158}$-detected galaxies at $6.8 \lesssim z \lesssim 7.7$. Six of our targets -- the primary sample -- are massive, UV-luminous galaxies drawn from the REBELS survey, while the remaining two are UV-fainter galaxies that were previously serendipitously detected through their luminous [CII] lines in the REBELS fields. We detect [OIII]$_{88}$ emission in all eight galaxies at $6.2 - 17.7σ$ significance, and find them to be consistent with the local dwarf galaxy relation between $L_\mathrm{[OIII]}$ and star formation rate. Our sample spans [OIII]/[CII] $\approx 1.9 - 9.6$, which is typical for the high-redshift galaxy population. Five of the primary targets benefit from JWST/NIRSpec observations, enabling a direct comparison of the [OIII]/[CII] ratio against rest-optical ISM diagnostics. We supplement our high-redshift sample with eleven $z\approx6-14$ galaxies in the literature for which similar ALMA and JWST observations are available, and furthermore compare to the [OIII]/[CII] ratios measured for local dwarf galaxies. We find that, at fixed metallicity and ionization parameter, $z>6$ galaxies show elevated [OIII]/[CII] ratios compared to local dwarfs. Instead, we find that a large [OIII]$_{4959,5007}$+H$β$ equivalent width -- a proxy for burstiness -- is the main driver of the high [OIII]/[CII] ratios seen in the early Universe, which is primarily due to [CII] being suppressed in bursty galaxies. Given the apparent validity of the [OIII]$_{88}$-SFR relation across most of cosmic time, as well as the abundance of young, bursty galaxies at high redshift, [OIII]$_{88}$ is set to remain a powerful ISM tracer at the cosmic dawn. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2509_16071 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | REBELS-IFU: on the origin of the elevated [OIII]/[CII] ratios in the early Universe Algera, Hiddo Rowland, Lucie Smit, Renske Fisher, Rebecca Ramambason, Lise Kumari, Nimisha Vallini, Livia Inami, Hanae Nanayakkara, Themiya Stefanon, Mauro Aravena, Manuel Bakx, Tom Bouwens, Rychard Bowler, Rebecca Cescon, Karin Chen, Chian-Chou Dayal, Pratika De Looze, Ilse Ferrara, Andrea Fudamoto, Yoshinobu Komarova, Lena van Leeuwen, Ivana Ormerod, Katherine Schouws, Sander Sommovigo, Laura Vijayan, Aswin Wang, Wei-Hao van der Werf, Paul Witstok, Joris Astrophysics of Galaxies We present new ALMA [OIII]$_{88}$ observations of eight previously [CII]$_{158}$-detected galaxies at $6.8 \lesssim z \lesssim 7.7$. Six of our targets -- the primary sample -- are massive, UV-luminous galaxies drawn from the REBELS survey, while the remaining two are UV-fainter galaxies that were previously serendipitously detected through their luminous [CII] lines in the REBELS fields. We detect [OIII]$_{88}$ emission in all eight galaxies at $6.2 - 17.7σ$ significance, and find them to be consistent with the local dwarf galaxy relation between $L_\mathrm{[OIII]}$ and star formation rate. Our sample spans [OIII]/[CII] $\approx 1.9 - 9.6$, which is typical for the high-redshift galaxy population. Five of the primary targets benefit from JWST/NIRSpec observations, enabling a direct comparison of the [OIII]/[CII] ratio against rest-optical ISM diagnostics. We supplement our high-redshift sample with eleven $z\approx6-14$ galaxies in the literature for which similar ALMA and JWST observations are available, and furthermore compare to the [OIII]/[CII] ratios measured for local dwarf galaxies. We find that, at fixed metallicity and ionization parameter, $z>6$ galaxies show elevated [OIII]/[CII] ratios compared to local dwarfs. Instead, we find that a large [OIII]$_{4959,5007}$+H$β$ equivalent width -- a proxy for burstiness -- is the main driver of the high [OIII]/[CII] ratios seen in the early Universe, which is primarily due to [CII] being suppressed in bursty galaxies. Given the apparent validity of the [OIII]$_{88}$-SFR relation across most of cosmic time, as well as the abundance of young, bursty galaxies at high redshift, [OIII]$_{88}$ is set to remain a powerful ISM tracer at the cosmic dawn. |
| title | REBELS-IFU: on the origin of the elevated [OIII]/[CII] ratios in the early Universe |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2509.16071 |