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VLA–ALMA spectroscopic survey in the hubble ultra deep field (VLASPECS) : total cold gas masses and CO Line ratios for z = 2–3 main-sequence galaxies.

Riechers, Dominik A. and Boogaard, Leindert A. and Decarli, Roberto and González-López, Jorge and Smail, Ian and Walter, Fabian and Aravena, Manuel and Carilli, Christopher L. and Cortes, Paulo C. and Cox, Pierre and Díaz-Santos, Tanio and Hodge, Jacqueline A. and Inami, Hanae and Ivison, Rob J. and Kaasinen, Melanie and Wagg, Jeff and Weiß, Axel and van der Werf, Paul (2020) 'VLA–ALMA spectroscopic survey in the hubble ultra deep field (VLASPECS) : total cold gas masses and CO Line ratios for z = 2–3 main-sequence galaxies.', Astrophysical journal., 896 (2). L21.


Using the NSF's Karl G. Jansky Very Large Array (VLA), we report six detections of CO(J = 1 → 0) emission and one upper limit in z = 2–3 galaxies originally detected in higher-J CO emission in the Atacama Large Millimeter/submillimeter Array Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS). From the CO(J = 1 → 0) line strengths, we measure total cold molecular gas masses of M gas = (2.4–11.6) × 1010 (α CO/3.6)M ⊙. We also measure a median CO(J = 3 → 2) to CO(J = 1 → 0) line brightness temperature ratio of r 31 = 0.84 ± 0.26, and a CO(J = 7 → 6) to CO(J = 1 → 0) ratio range of r 71 < 0.05 to r 71 = 0.17. These results suggest that CO(J = 3 → 2) selected galaxies may have a higher CO line excitation on average than CO(J = 1 → 0) selected galaxies, based on the limited, currently available samples from the ASPECS and VLA CO Luminosity Density at High Redshift (COLDz) surveys. This implies that previous estimates of the cosmic density of cold gas in galaxies based on CO(J = 3 → 2) measurements should be revised down by a factor of sime2 on average based on assumptions regarding CO excitation alone. This correction further improves the agreement between the best currently existing constraints on the cold gas density evolution across cosmic history from line scan surveys, and the implied characteristic gas depletion times.

Item Type:Article
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Publisher statement:© 2020. The American Astronomical Society. All rights reserved.
Date accepted:19 May 2020
Date deposited:09 July 2020
Date of first online publication:15 June 2020
Date first made open access:09 July 2020

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