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Dust, CO, and [C I]: cross-calibration of molecular gas mass tracers in metal-rich galaxies across cosmic time

Dunne, L. ORCID:, Maddox, S. J. ORCID:, Papadopoulos, P. P. ORCID:, Ivison, R. J. and Gomez, H. L. ORCID: 2022. Dust, CO, and [C I]: cross-calibration of molecular gas mass tracers in metal-rich galaxies across cosmic time. Monthly Notices of the Royal Astronomical Society 517 (1) , 962–999. 10.1093/mnras/stac2098

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We present a self-consistent cross-calibration of the three main molecular gas mass tracers in galaxies, namely the 12CO(1–0), [C I](3P1–3P0) lines, and the submm dust continuum emission, using a sample of 407 galaxies, ranging from local discs to submillimetre-selected galaxies (SMGs) up to z ≈ 6. A Bayesian statistical method is used to produce galaxy-scale universal calibrations of these molecular gas indicators, that hold over 3–4 orders of magnitude in infrared luminosity, LIR. Regarding the dust continuum, we use a mass-weighted dust temperature, Tmw, determined using new empirical relations between temperature and luminosity. We find the average L/Mmol gas mass conversion factors (including He) to be α850=6.9×1012WHz−1M−1⊙ ⁠, αCO = 4.0 M⊙ (κ km s−1 pc2)−1, and αCI = 17.0 M⊙ (κ km s−1 pc2)−1, based on the assumption that the mean dust properties of the sample (κH = gas-to-dust ratio/dust emissivity) will be similar to those of local metal rich galaxies and the Milky Way. The tracer with the least intrinsic scatter is [C I](1–0), while CO(1–0) has the highest. The conversion factors show a weak but significant correlation with LIR which is not apparent when Tmw is held constant. Assuming dust properties typical of metal-rich galaxies, we infer a neutral carbon abundance XCI=[C0/H2]=1.6×10−5 ⁠, similar to that in the Milky Way. We find no evidence for bi-modality of αCO between main-sequence (MS) galaxies and those with extreme star-formation intensity, i.e. ultraluminous infrared galaxies (ULIRGs) and SMGs. The means of the three conversion factors are found to be similar between MS galaxies and ULIRGs/SMGs, to within 10–20 per cent. The overarching conclusion of our work is that, for metal-rich galaxies, near-universal average values for αCO, XCI ⁠, and κH are adequate for global molecular gas estimates within the expected uncertainties. The 1σ scatter in our optimized values for αCO, XCI ⁠, and κH are 0.14, 0.11, and 0.15 dex, respectively.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Publisher: Oxford University Press
ISSN: 0035-8711
Funders: ERC
Date of First Compliant Deposit: 15 May 2023
Date of Acceptance: 25 July 2022
Last Modified: 24 May 2023 07:17

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