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 $\gtrsim 12$ submillimeter galaxies (SMGs) at $z=4.3$, to study its integrated molecular gas content via CO(4-3) and long-wavelength dust continuum. The $\sim$30-hour integration represents one of the longest exposures yet taken on a single pointing with the ACA 7-m. The low-resolution ACA data ($21.0^{\prime \prime }\times 12.2^{\prime \prime }$) reveal a 75% excess CO(4-3) flux compared to the sum of individual sources detected in higher-resolution Atacama Large Millimeter Array (ALMA) data ($1.0^{\prime \prime }\times 0.8^{\prime \prime }$). Our work also reveals a similar result by tapering the ALMA data to $10^{\prime \prime }$. In contrast, the 3.2mm dust continuum shows little discrepancy between ACA and ALMA. A single-dish [CII] spectrum obtained by APEX/FLASH supports the ACA CO(4-3) result, revealing a large excess in [CII] 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 circum-galactic medium (CGM) or the pre-heated proto-intracluster medium (proto-ICM). If this molecular gas reservoir replenishes the star formation fuel, the overall depletion timescale will exceed 400Myr, reducing the requirement for the simultaneous SMG activity in SPT2349$-$56. Our results highlight the role of an extended gas reservoir in sustaining a high star formation rate (SFR) in SPT2349$-$56, and potentially establishing the ICM during the transition phase to a mature cluster.

14 pages, 6 figures and 3 tables. ApJL in press

References in corpus (39)

• Array Programming with NumPy
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• Mass and environment as drivers of galaxy evolution in SDSS and zCOSMOS and the origin of the Schechter function
• CASA, the Common Astronomy Software Applications for Radio Astronomy
• Bias-free Measurement of Giant Molecular Cloud Properties
• A massive proto-cluster of galaxies at a redshift of z {\approx} 5.3
• High-redshift star formation in the ALMA era
• PHANGS-ALMA Data Processing and Pipeline
• The ALPINE-ALMA [CII] survey: Star-formation-driven outflows and circumgalactic enrichment in the early Universe
• The nature of the [CII] emission in dusty star-forming galaxies from the SPT survey
• Molecular outflows in local galaxies: Method comparison and a role of intermittent AGN driving
• The Rest-Frame Submillimeter Spectrum of High-Redshift, Dusty, Star-Forming Galaxies
• The Complete Redshift Distribution of Dusty Star-forming Galaxies from the SPT-SZ Survey
• Molecular Gas in the Halo Fuels the Growth of a Massive Cluster Galaxy at High Redshift
• Dust, CO and [CI]: Cross-calibration of molecular gas mass tracers in metal-rich galaxies across cosmic time
• No evidence for [CII] halos or high-velocity outflows in z>6 quasar host galaxies
• The DIANOGA simulations of galaxy clusters: characterizing star formation in proto-clusters
• Molecular gas in z~6 quasar host galaxies
• The Young and the Wild: What happens to Protoclusters forming at z = 4?
• Outflows from Super Star Clusters in the Central Starburst of NGC253
• Is there enough star formation in simulated protoclusters?
• SUPER. VI. A giant molecular halo around a z~2 quasar
• The Infrared Luminosity of Galaxy Clusters
• Overdensities of Submillimetre-Bright Sources around Candidate Protocluster Cores Selected from the South Pole Telescope Survey
• A cosmic stream of atomic carbon gas connected to a massive radio galaxy at redshift 3.8
• VLA Legacy Survey of Molecular Gas in Massive Star-forming Galaxies at High Redshift
• Optical and near-infrared observations of the SPT2349-56 proto-cluster core at z = 4.3
• Rapid build-up of the stellar content in the protocluster core SPT2349$-$56 at $z=4.3$
• The cold circumgalactic environment of MAMMOTH-I: dynamically cold gas in the core of an Enormous Ly-alpha Nebula
• The ALMA-CRISTAL survey. Discovery of a 15 kpc-long gas plume in a $z=4.54$ Lyman-$\alpha$ blob
• Observational Evidence for Large-Scale Gas Heating in a Galaxy Protocluster at z=2.30
• Fast SMBH growth in the SPT2349--56 protocluster at $z=4.3$
• An investigation of the circumgalactic medium around z~2.2 AGN with ACA and ALMA
• ALMA unveils wider environment of distant red protocluster core
• The Manhattan Suite: Accelerated galaxy evolution in the early Universe
• Star Formation and Chemical Enrichment in Protoclusters
• Kinematic analysis of $\mathbf{z}=4.3$ galaxies in the SPT2349$-$56 protocluster core
• CO survey of high-z radio galaxies, revisited with ALMA: Jet-cloud Alignments and Synchrotron Brightening by Molecular Gas in the Circumgalactic Environment
• A possible relation between global CO excitation and massive molecular outflows in local ULIRGs

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