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A large molecular gas reservoir in the protocluster SPT2349−56 at z  = 4.3

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DOIResolve DOI: https://doi.org/10.3847/2041-8213/adb8d8
AuthorSearch for: ORCID identifier: https://orcid.org/0000-0002-6922-469X; Search for: 1ORCID identifier: https://orcid.org/0000-0002-8487-3153; Search for: ORCID identifier: https://orcid.org/0000-0002-3187-1648; Search for: ORCID identifier: https://orcid.org/0009-0008-8718-0644; Search for: ORCID identifier: https://orcid.org/0000-0002-6290-3198; Search for: ORCID identifier: https://orcid.org/0000-0003-2860-5717; Search for: ORCID identifier: https://orcid.org/0000-0002-4657-7679; Search for: ORCID identifier: https://orcid.org/0000-0002-2367-1080; Search for: ORCID identifier: https://orcid.org/0000-0001-7946-557X; Search for: ORCID identifier: https://orcid.org/0000-0001-7477-1586; Search for: ORCID identifier: https://orcid.org/0000-0001-6629-0379; Search for: ORCID identifier: https://orcid.org/0000-0003-3256-5615; Search for: ORCID identifier: https://orcid.org/0000-0001-7192-3871; Search for: ORCID identifier: https://orcid.org/0000-0001-7610-5544; Search for: ORCID identifier: https://orcid.org/0009-0003-4626-9777; Search for: ORCID identifier: https://orcid.org/0000-0003-4678-3939
Affiliation
  1. National Research Council of Canada. Herzberg Astronomy and Astrophysics
FunderSearch for: Natural Sciences and Engineering Research Council of Canada
FormatText, Article
Subjectsubmillimeter astronomy; galaxy evolution; high-redshift galaxies
Abstract
We present Atacama Compact Array (ACA) Band-3 observations of the protocluster SPT2349−56, an extreme system hosting >10 ultraluminous infrared galaxies (ULIRGs; LIR ≳ 10¹²L⊙) in a 200 kpc diameter region at z = 4.3, to study its integrated molecular gas content via CO(4–3) and the long-wavelength dust continuum. The ∼30 hr integration represents one of the longest exposures yet taken on a single pointing with the ACA 7 m. The low-resolution ACA data (21".0 × 12".2) reveal a 75% excess CO(4–3) flux compared to the sum of individual sources detected in higher-resolution Atacama Large Millimeter/submillimeter Array (ALMA) data (1".0 × 0".8). Our work also reveals a similar result by tapering the ALMA data to 10''. In contrast, the 3.2 mm dust continuum shows little discrepancy between ACA and ALMA. A single-dish [C ii] spectrum obtained by APEX/FLASH supports the ACA CO(4–3) result, revealing a large excess in [C ii] emission relative to ALMA. The missing flux is unlikely due to undetected faint sources but instead suggests that high-resolution ALMA observations might miss extended and low-surface-brightness gas. Such emission could originate from the circumgalactic medium or the preheated protointracluster medium (proto-ICM). If this molecular gas reservoir replenishes the star formation fuel, the overall depletion timescale will exceed 400 Myr, reducing the requirement for the simultaneous ULIRG activity in SPT2349−56. Our results highlight the role of an extended gas reservoir in sustaining a high star formation rate in SPT2349−56 and potentially establishing the ICM during the transition phase to a mature cluster.
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  • The Astrophysical Journal Letters 982, no. 1, L17 (17 March 2025).
LanguageEnglish
Peer reviewedYes
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Record identifierfcaaf73c-3a54-4765-b258-1caa7dc3c0b4
Record created2025-05-29
Record modified2025-05-29
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