Extended warm and dense gas towards W49A: starburst conditions in our Galaxy?
Bibliographic record
Abstract
\n Context. The star formation rates in starburst galaxies are orders of magnitude higher than in local star-forming regions, and the origin of this difference is not well understood.\n Aims. We use sub-mm spectral line maps to characterize the physical conditions of the molecular gas in the luminous Galactic star-forming region W49A and compare them with the conditions in starburst galaxies.\n Methods. We probe the temperature and density structure of W49A using H2CO and HCN line ratios over a 2′ × 2′ (6.6 × 6.6 pc) field with an angular resolution of 15′′ (~0.8 pc) provided by the JCMT Spectral Legacy Survey. We analyze the rotation diagrams of lines with multiple transitions with corrections for optical depth and beam dilution, and estimate excitation temperatures and column densities.\n Results. Comparing the observed line intensity ratios with non-LTE radiative transfer models, our results reveal an extended region (about 1′ × 1′, equivalent to ~3 × 3 pc at the distance of W49A) of warm (>100 K) and dense (> 105 cm-3) molecular gas, with a mass of 2 × 104 − 2 × 105 M⊙ (by applying abundances derived for other regions of massive star-formation). These temperatures and densities in W49A are comparable to those found in clouds near the center of the Milky Way and in starburst galaxies.\n Conclusions. The highly excited gas is likely to be heated via shocks from the stellar winds of embedded, O-type stars or alternatively due to UV irradiation, or possibly a combination of these two processes. Cosmic rays, X-ray irradiation and gas-grain collisional heating are less likely to be the source of the heating in the case of W49A. \n
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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 | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| 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".