New Insights into the Physical Conditions and Internal Structure of a Candidate Proto-globular Cluster
Bibliographic record
Abstract
Abstract We present ∼0.″1 resolution (∼10 pc) Atacama Large Millimeter/submillimeter Array observations of a molecular cloud identified in the merging Antennae galaxies with the potential to form a globular cluster, nicknamed the “Firecracker.” Since star formation has not yet begun at an appreciable level in this region, this cloud provides an example of what the birth environment of a globular cluster may have looked like before stars formed and disrupted the natal physical conditions. Using emission from 12CO(2–1), 12CO(3–2), 13CO(2–1), HCN(4–3), and HCO+(4–3) molecular lines, we are able to resolve the cloud’s structure and find that it has a characteristic radius of 22 pc and a mass of (1–9) × 106 M ⊙. We also put constraints on the abundance ratios 12CO/13CO and H2/12CO. Based on the calculation of the mass, we determine that the commonly used CO-to-H2 conversion factor in this region varies spatially, with average values in the range cm−2 (K km s−1)−1. We demonstrate that if the cloud is bound (as is circumstantially suggested by its bright, compact morphology), an external pressure in excess of P/k > 108 K cm−3 is required. This would be consistent with theoretical expectations that globular cluster formation requires high-pressure environments, much higher than typical values found in the Milky Way. The position–velocity diagram of the cloud and its surrounding material suggests that this high pressure may be produced by ram pressure from the collision of filaments. The radial profile of the column density can be fit with both a Gaussian and a Bonnor–Ebert profile. If the Bonnor–Ebert fit is taken to be indicative of the cloud’s physical structure, it would imply the cloud is gravitationally stable and pressure-confined. The relative line strengths of HCN and HCO+ in this region also suggest that these molecular lines can be used as a tracer for the evolutionary stage of a 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 | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
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".