@article{c85c3c7013cb402d806ab35f89bb73ed,
title = "A Large Molecular Gas Reservoir in the Protocluster SPT2349−56 at z = 4.3",
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.",
author = "Dazhi Zhou and Chapman, {Scott C.} and Nikolaus Sulzenauer and Ryley Hill and Manuel Aravena and Pablo Araya-Araya and Jared Cathey and Marrone, {Daniel P.} and Phadke, {Kedar A.} and Cassie Reuter and Manuel Solimano and Spilker, {Justin S.} and Vieira, {Joaquin D.} and David Vizgan and Wang, {George C.P.} and Axel Weiss",
note = "We thank John E. Carlstrom, Kevin Harrington, Daizhong Liu, Padelis Papadopoulos, and Douglas Rennehan for useful discussions on this work. This research used the Canadian Advanced Network For Astronomy Research (CANFAR) operated in partnership by the Canadian Astronomy Data Centre and The Digital Research Alliance of Canada with support from the National Research Council of Canada, the Canadian Space Agency, CANARIE, and the Canadian Foundation for Innovation. This Letter makes use of the following ALMA data: ADS/JAO.ALMA#2017.1.00273.S, ADS/JAO.ALMA#2018.1.00058.S, and ADS/JAO.ALMA#2023.1.00124.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This publication is based on data acquired with the Atacama Pathfinder Experiment (APEX). APEX is a collaboration between the Max-Planck-Institut fur Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory. The SPT is supported by the National Science Foundation through grant PLR-1248097, with partial support through PHY-1125897, the Kavli Foundation, and the Gordon and Betty Moore Foundation grant GBMF 947. D.Z., S.C.C., R.H., and G.C.P.W. acknowledge support from NSERC-6740. M.A. acknowledges support from ANID Basal Project FB210003 and ANID MILENIO NCN2024_112. M.S. was financially supported by Becas-ANID scholarship #21221511 and also acknowledges support from ANID BASAL project FB210003.",
year = "2025",
month = mar,
day = "20",
doi = "10.3847/2041-8213/adb8d8",
language = "English (US)",
volume = "982",
journal = "Astrophysical Journal Letters",
issn = "2041-8205",
publisher = "American Astronomical Society",
number = "1",
}