ALMA observations of pre- JWST z ~ 10 galaxy candidates: A CO( J = 9–8) line from a ULIRG at z = 2.54 and revisit of the photometric redshifts with JWST photometry

Abstract We present Atacama Large Millimetre/submillimetre Array (ALMA) observations targeting the [O iii] $88\, \umu$m line for six z ~ 10 galaxy candidates selected with the Hubble Space Telescope and the Spitzer Space Telescope. We detect a line (4.5σ) and dust continuum emission (30σ) in UDS_18697, while detecting neither robust line nor continuum emission in the remaining five objects. The detected line in UDS_18697 is identified as CO(J = 9–8), because follow-up James Webb Space Telescope (JWST) NIRSpec observations have confirmed the redshift as z = 2.54. UDS_18697 is classified as an ultra luminous infrared galaxy (ULIRG) with far-infrared (FIR) luminosity of LFIR ≈ 1.1 × 1012 L⊙, assuming a dust temperature of Td ≈ 42 K, estimated using a physically-motivated method. We find that UDS_18697 follows the $L_{FIR}-L^{\prime }_{CO}$ relation for local and z > 2 galaxies, albeit being slightly brighter in CO(J = 9–8). Also, based on the follow-up NIRSpec observations and spectral energy distribution fitting using JWST/NIRCam photometry, we found that most of our targets are suggested to be low-z interlopers. Motivated by these redshift misclassifications, we investigate colour–colour selection criteria for high-z galaxies using JWST spectroscopic survey catalogues. We find that elevating a colour threshold tracing the Lyman break is crucial for constructing a robust high-z sample, particularly for wide field surveys such as Euclid Deep Fields and Roman High-Latitude Wide-Area Survey.

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Journal
Monthly Notices of the Royal Astronomical Society
Published
2026-08-20
DOI
https://doi.org/10.1093/mnras/stag1546
Primary Topic
Galaxies: Formation, Evolution, Phenomena
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article
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article

ALMA observations of pre- JWST z ~ 10 galaxy candidates: A CO( J = 9–8) line from a ULIRG at z = 2.54 and revisit of the photometric redshifts with JWST photometry

Seiji Fujimoto, Yoichi Tamura, Yuma Sugahara, Charles L. Steinhardt et al.
Monthly Notices of the Royal Astronomical Society
Galaxies: Formation, Evolution, Phenomena
article

ALMA observations of pre- JWST z ~ 10 galaxy candidates: A CO( J = 9–8) line from a ULIRG at z = 2.54 and revisit of the photometric redshifts with JWST photometry

Seiji Fujimoto, Yoichi Tamura, Yuma Sugahara, Charles L. Steinhardt, Rebecca L. Larson, Yuichi Harikane, Larry Bradley, Ken Mawatari, Takuya Hashimoto, John R. Weaver, Yi W. Ren, Takahiro Morishita, Akio Inoue, Nima Chartab, Suzuka Arai, David B Sanders, Steven L Finkelstein, Andreas Faisst
article en

Abstract

Abstract We present Atacama Large Millimetre/submillimetre Array (ALMA) observations targeting the [O iii] $88\, \umu$m line for six z ~ 10 galaxy candidates selected with the Hubble Space Telescope and the Spitzer Space Telescope. We detect a line (4.5σ) and dust continuum emission (30σ) in UDS_18697, while detecting neither robust line nor continuum emission in the remaining five objects. The detected line in UDS_18697 is identified as CO(J = 9–8), because follow-up James Webb Space Telescope (JWST) NIRSpec observations have confirmed the redshift as z = 2.54. UDS_18697 is classified as an ultra luminous infrared galaxy (ULIRG) with far-infrared (FIR) luminosity of LFIR ≈ 1.1 × 1012 L⊙, assuming a dust temperature of Td ≈ 42 K, estimated using a physically-motivated method. We find that UDS_18697 follows the $L_{FIR}-L^{\prime }_{CO}$ relation for local and z > 2 galaxies, albeit being slightly brighter in CO(J = 9–8). Also, based on the follow-up NIRSpec observations and spectral energy distribution fitting using JWST/NIRCam photometry, we found that most of our targets are suggested to be low-z interlopers. Motivated by these redshift misclassifications, we investigate colour–colour selection criteria for high-z galaxies using JWST spectroscopic survey catalogues. We find that elevating a colour threshold tracing the Lyman break is crucial for constructing a robust high-z sample, particularly for wide field surveys such as Euclid Deep Fields and Roman High-Latitude Wide-Area Survey.

Monthly Notices of the Royal Astronomical Society
University of Hawaiʻi at Mānoa (US), California Institute of Technology (US), Space Telescope Science Institute (US), University of Tsukuba (JP), Waseda University (JP), Tohoku University (JP), Kavli Institute for Particle Astrophysics and Cosmology (US), Canadian Institute for Theoretical Astrophysics (CA), Université Bourgogne Franche-Comté (FR), Nagoya University (JP), The University of Tokyo (JP), University of Missouri (US), The University of Texas at Austin (US)
National Science Foundation, Brinson Foundation, National Radio Astronomy Observatory, Ministry of Education, Culture, Sports, Science and Technology, Korea Astronomy and Space Science Institute, Waseda University, National Astronomical Observatory of Japan, Japan Society for the Promotion of Science, National Institutes of Natural Sciences
Affordable and clean energy
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Galaxies: Formation, Evolution, Phenomena
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