ALMA Chemical Evolution (ACE) Survey: Molecular gas properties of low-mass, low-metallicity galaxies at cosmic noon
Abstract
Molecular gas plays a central role in regulating star formation and galaxy evolution, yet observational constraints at cosmic noon remain biased toward massive, metal-rich systems. We present ALMA Band 3 observations of the CO J=3-2 transition in 26 unlensed star-forming galaxies from the ALMA Chemical Evolution (ACE) Large Program at z~2-2.5, probing stellar masses of 109 < M⋆ < 1010.5 M⊙ and sub-solar metallicities (8.2 < 12 + log(O/H) < 8.6). We derived molecular gas masses using a metallicity-dependent CO-to-H2 conversion factor and alongside analysed stacking measurements and a homogenized literature compilation spanning both local and high-redshift galaxies. We find that the ACE galaxies extend established molecular-gas scaling relations to an order of magnitude lower stellar masses than previously explored at cosmic noon. The molecular gas mass (Mmol) correlates tightly with star formation rate (SFR), while molecular gas fractions show a strong dependence on specific star formation rate (sSFR) and offset from the star-forming main sequence. In contrast, molecular gas fractions show only weak trends with stellar mass and no significant dependence on metallicity. Molecular gas depletion times are ~1 Gyr and vary little with stellar mass or metallicity, and weakly with sSFR and offset from the star-forming main sequence. Together this further reinforces that the availability of molecular gas is the primary driver of the SFR in galaxies, with changes in star-formation efficiency playing a secondary role. Leveraging the expanded parameter space probed by the ACE and literature samples, we derive a new empirical prescription for predicting Mmol as a function of SFR and sSFR. The persistence of the observed scaling relations suggests a largely universal framework governing the molecular gas-star formation cycle across cosmic time.
Related
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- ALMA Chemical Evolution (ACE) survey: The gas fundamental metallicity relation at cosmic noon
BibTeX
@misc{popping2026alma,
title = {{ALMA Chemical Evolution (ACE) Survey: Molecular gas properties of low-mass, low-metallicity galaxies at cosmic noon}},
author = {Gergő Popping and Ivanna Langan and Nikki N. Geesink and Melanie Kaasinen and Irene Shivaei and Leindert A. Boogaard and Daizhong Liu and Max Parente and Alexandra Pope and Roxana Popescu and Manuel Solimano and Bahram Mobasher and Bianca Moreschini and Desika Narayanan and Naveen Reddy and Ryan L. Sanders},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.21072},
eprint = {2609.21072},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.21072},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - ALMA Chemical Evolution (ACE) Survey: Molecular gas properties of low-mass, low-metallicity galaxies at cosmic noon
AU - Gergő Popping
AU - Ivanna Langan
AU - Nikki N. Geesink
AU - Melanie Kaasinen
AU - Irene Shivaei
AU - Leindert A. Boogaard
AU - Daizhong Liu
AU - Max Parente
AU - Alexandra Pope
AU - Roxana Popescu
AU - Manuel Solimano
AU - Bahram Mobasher
AU - Bianca Moreschini
AU - Desika Narayanan
AU - Naveen Reddy
AU - Ryan L. Sanders
PY - 2026
DA - 2026/09/17
PB - arXiv
DO - 10.48550/arxiv.2609.21072
UR - https://arxiv.org/abs/2609.21072
AB - Molecular gas plays a central role in regulating star formation and galaxy evolution, yet observational constraints at cosmic noon remain biased toward massive, metal-rich systems. We present ALMA Band 3 observations of the CO J=3-2 transition in 26 unlensed star-forming galaxies from the ALMA Chemical Evolution (ACE) Large Program at z~2-2.5, probing stellar masses of 10^9 < M_⋆ < 10^10.5 M_⊙ and sub-solar metallicities (8.2 < 12 + log(O/H) < 8.6). We derived molecular gas masses using a metallicity-dependent CO-to-H_2 conversion factor and alongside analysed stacking measurements and a homogenized literature compilation spanning both local and high-redshift galaxies. We find that the ACE galaxies extend established molecular-gas scaling relations to an order of magnitude lower stellar masses than previously explored at cosmic noon. The molecular gas mass (M_mol) correlates tightly with star formation rate (SFR), while molecular gas fractions show a strong dependence on specific star formation rate (sSFR) and offset from the star-forming main sequence. In contrast, molecular gas fractions show only weak trends with stellar mass and no significant dependence on metallicity. Molecular gas depletion times are ~1 Gyr and vary little with stellar mass or metallicity, and weakly with sSFR and offset from the star-forming main sequence. Together this further reinforces that the availability of molecular gas is the primary driver of the SFR in galaxies, with changes in star-formation efficiency playing a secondary role. Leveraging the expanded parameter space probed by the ACE and literature samples, we derive a new empirical prescription for predicting M_mol as a function of SFR and sSFR. The persistence of the observed scaling relations suggests a largely universal framework governing the molecular gas-star formation cycle across cosmic time.
ER -