A Large Molecular Gas Reservoir in the Protocluster SPT2349−56 at <i>z</i> = 4.3
Bibliographic record
Abstract
Abstract We present Atacama Compact Array (ACA) Band-3 observations of the protocluster SPT2349−56, an extreme system hosting >10 ultraluminous infrared galaxies (ULIRGs; L IR ≳ 1012 L ⊙) 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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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".