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Dust continuum, CO, and  [C I] 1 − 0 lines: self-consistent H2 mass estimates and the possibility of globally CO-‘dark’ galaxies at z = 0.35

Dunne, L. ORCID:, Maddox, S. J. ORCID:, Vlahakis, C. and Gomez, H. L. ORCID: 2021. Dust continuum, CO, and  [C I] 1 − 0 lines: self-consistent H2 mass estimates and the possibility of globally CO-‘dark’ galaxies at z = 0.35. Monthly Notices of the Royal Astronomical Society 501 (2) , pp. 2573-2607. 10.1093/mnras/staa3526

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We present Atacama Large Millimetre Array observations of a small but statistically complete sample of 12 250-μm-selected galaxies at z = 0.35 designed to measure their dust submillimeter continuum emission as well as their  12CO(1−0) and atomic carbon  [C I](3P1−3P0) spectral lines. This is the first sample of galaxies with global measures of all three H2-mass tracers and that shows star formation rates (4–26 M⊙ yr−1) and infrared luminosities (⁠1−6×1011L⊙⁠) typical of star-forming galaxies in their era. We find a surprising diversity of morphology and kinematic structure; one third of the sample have evidence for interaction with nearby smaller galaxies, several sources have disjoint dust and gas morphology. Moreover, two galaxies have very high  L′CI / L′CO ratios for their global molecular gas reservoirs; if confirmed, such extreme intensity ratios in a sample of dust-selected, massive star-forming galaxies present a challenge to our understanding of interstellar medium. Finally, we use the emission of the three molecular gas tracers, to determine the carbon abundance,  XCI , and CO–H2 conversion  αCO in our sample, using a weak prior that the gas-to-dust ratio is similar to that of the Milky Way for these massive and metal-rich galaxies. Using a likelihood method that simultaneously uses all three gas tracer measurements, we find mean values and errors on the mean of ⟨αCO⟩=3.0±0.5M⊙(Kkms−1pc2)−1 and ⟨XCI⟩=1.6±0.1×10−5 (or αCI=18.8M⊙(Kkms−1pc2)−1⁠) and δGDR=128±16 (or α850=5.9×1012WHz−1M⊙−1⁠), where our starting assumption is that these metal-rich galaxies have an average gas-to-dust ratio similar to that of the Milky Way centred on δGDR=135⁠.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Publisher: Oxford University Press
ISSN: 0035-8711
Date of First Compliant Deposit: 12 February 2021
Date of Acceptance: 9 November 2020
Last Modified: 05 May 2023 19:47

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