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Published February 1, 2022 | Accepted Version + Published
Journal Article Open

Molecular Gas Excitation of the Massive Dusty Starburst CRLE and the Main-sequence Galaxy HZ10 at z = 5.7 in the COSMOS Field


We report CO(5 → 4) and CO(6 → 5) line observations in the dusty starbursting galaxy CRLE (z = 5.667) and the main-sequence (MS) galaxy HZ10 (z = 5.654) with the Northern Extended Millimeter Array. CRLE is the most luminous z > 5 starburst in the COSMOS field and HZ10 is the most gas-rich "normal" galaxy currently known at z > 5. We find line luminosities for CO(5 → 4) and CO(6 → 5) of (4.9 ± 0.5) and (3.8 ± 0.4) × 10¹⁰ K km s⁻¹ pc² for CRLE and upper limits of 10 K km s⁻¹ pc² for HZ10, respectively. The CO excitation of CRLE appears comparable to other z > 5 dusty star-forming galaxies. For HZ10, these line luminosity limits provide the first significant constraints of this kind for an MS galaxy at z > 5. We find the upper limit of L′_(5→4)/L′_(2→1) in HZ10 could be similar to the average value for MS galaxies around z ≈ 1.5, suggesting that MS galaxies with comparable gas excitation may already have existed one billion years after the Big Bang. For CRLE we determine the most likely values for the H2 density, kinetic temperature, and dust temperature based on excitation modeling of the CO line ladder. We also derive a total gas mass of (7.1 ± 1.3) × 10¹⁰ M_⊙. Our findings provide some of the currently most detailed constraints on the gas excitation that sets the conditions for star formation in a galaxy protocluster environment at z > 5.

Additional Information

© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2021 October 11; revised 2021 November 26; accepted 2021 December 4; published 2022 February 3. D.V. and D.R. acknowledge support from the National Science Foundation under grant numbers AST- 1614213 and AST-1910107. D.R. also acknowledges support from the Alexander von Humboldt Foundation through a Humboldt Research Fellowship for Experienced Researchers. This work is based on observations carried out under project number S18DK with the IRAM NOEMA Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). The authors thank Ian Smail and James Geach for providing an updated flux measurement from the SCUBA-2 COSMOS survey and Christian Henkel for the original version of the LVG code.

Attached Files

Published - Vieira_2022_ApJ_925_174.pdf

Accepted Version - 2112.11705.pdf


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August 22, 2023
October 23, 2023