Multi-tracer exploration of molecular gas in main sequence galaxies at z~4.5
Abstract
Molecular gas masses in high-z galaxies are inferred from indirect tracers, whose respective reliability remains poorly constrained. In particular, the bright [CII] 158μm line is now widely used as a molecular gas tracer at z>4, yet direct observational tests against CO remain scarce. We search for CO(4-3), CO(5-4), and [CI](1-0) lines in three of the most [CII]-luminous galaxies at z~4.5 from the ALPINE survey to assess the detectability of these lines in high-z main-sequence (MS) galaxies and to test the reliability of [CII] emission as a molecular gas tracer through the cross-comparison of molecular gas masses inferred from six tracers: CO(4-3), CO(5-4), [CI](1-0), [CII], dust continuum, and [CII]-based dynamical mass, adopting standard calibrations and conversion factors. We detect CO(4-3) and CO(5-4) lines at high significance in the near-solar metallicity galaxy DC873756, obtain a tentative CO(4-3) detection in the merging system DC818760, and detect no CO emission in the half-solar metallicity galaxy VC5110377875. [CI] remains undetected in all three galaxies. In DC873756 the molecular gas masses inferred from the six considered tracers agree within their uncertainties despite different systematics inherent to each tracer. The agreement suggests that, at least for some near-solar metallicity MS galaxies at z~4.5, the CO SLED and Milky Way CO-to-H2 conversion factor adopted for MS galaxies at cosmic noon remain applicable and that mid-J CO transitions trace a substantial fraction of the molecular gas reservoir. The CO non-detection in VC5110377875 is consistent with the reduced CO detectability expected at lower metallicities. In DC818760 we find an inconsistency between the [CII]-based molecular gas mass and masses derived from the other tracers, indicating a [CII] excess possibly reflecting enhanced emission from shocks and/or diffuse ionized gas in merger-driven conditions.
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BibTeX
@misc{dessaugeszavadsky2026multitracer,
title = {{Multi-tracer exploration of molecular gas in main sequence galaxies at z~4.5}},
author = {M. Dessauges-Zavadsky and M. Béthermin and M. Ginolfi and L. Vallini and A. Faisst and M. -Y. Xiao and F. Pozzi and P. Cassata and Y. Fudamoto and C. Gruppioni and G. C. Jones and M. Kohandel and G. Rodighiero and M. Romano and P. Theulé and G. Zamorani and C. Accard and C. Guillaume},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.03166},
eprint = {2609.03166},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.03166},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Multi-tracer exploration of molecular gas in main sequence galaxies at z~4.5
AU - M. Dessauges-Zavadsky
AU - M. Béthermin
AU - M. Ginolfi
AU - L. Vallini
AU - A. Faisst
AU - M. -Y. Xiao
AU - F. Pozzi
AU - P. Cassata
AU - Y. Fudamoto
AU - C. Gruppioni
AU - G. C. Jones
AU - M. Kohandel
AU - G. Rodighiero
AU - M. Romano
AU - P. Theulé
AU - G. Zamorani
AU - C. Accard
AU - C. Guillaume
PY - 2026
DA - 2026/09/02
PB - arXiv
DO - 10.48550/arxiv.2609.03166
UR - https://arxiv.org/abs/2609.03166
AB - Molecular gas masses in high-z galaxies are inferred from indirect tracers, whose respective reliability remains poorly constrained. In particular, the bright [CII] 158μm line is now widely used as a molecular gas tracer at z>4, yet direct observational tests against CO remain scarce. We search for CO(4-3), CO(5-4), and [CI](1-0) lines in three of the most [CII]-luminous galaxies at z~4.5 from the ALPINE survey to assess the detectability of these lines in high-z main-sequence (MS) galaxies and to test the reliability of [CII] emission as a molecular gas tracer through the cross-comparison of molecular gas masses inferred from six tracers: CO(4-3), CO(5-4), [CI](1-0), [CII], dust continuum, and [CII]-based dynamical mass, adopting standard calibrations and conversion factors. We detect CO(4-3) and CO(5-4) lines at high significance in the near-solar metallicity galaxy DC873756, obtain a tentative CO(4-3) detection in the merging system DC818760, and detect no CO emission in the half-solar metallicity galaxy VC5110377875. [CI] remains undetected in all three galaxies. In DC873756 the molecular gas masses inferred from the six considered tracers agree within their uncertainties despite different systematics inherent to each tracer. The agreement suggests that, at least for some near-solar metallicity MS galaxies at z~4.5, the CO SLED and Milky Way CO-to-H2 conversion factor adopted for MS galaxies at cosmic noon remain applicable and that mid-J CO transitions trace a substantial fraction of the molecular gas reservoir. The CO non-detection in VC5110377875 is consistent with the reduced CO detectability expected at lower metallicities. In DC818760 we find an inconsistency between the [CII]-based molecular gas mass and masses derived from the other tracers, indicating a [CII] excess possibly reflecting enhanced emission from shocks and/or diffuse ionized gas in merger-driven conditions.
ER -