THE DENSE GAS IN THE LARGEST MOLECULAR COMPLEXES OF THE ANTENNAE: HCN AND HCO<sup>+</sup> OBSERVATIONS OF NGC 4038/39 USING ALMA
Bibliographic record
Abstract
ABSTRACT We present observations of the dense molecular gas tracers <?CDATA $\mathrm{HCN}$?> , <?CDATA $\mathrm{HNC}$?> , and <?CDATA ${\mathrm{HCO}}^{+}$?> in the <?CDATA $J=1-0$?> transition using the Atacama Large Millimeter/submillimeter Array. We supplement our data sets with previous observations of <?CDATA $\mathrm{CO}$?> <?CDATA $J=1-0$?> , which trace the total molecular gas content. We separate the Antennae into seven bright regions in which we detect emission from all three molecules, including the nuclei of NGC 4038 and NGC 4039, five super giant molecular complexes in the overlap region, and two additional bright clouds. We find that the ratio of <?CDATA ${L}_{\mathrm{HCN}}/{L}_{\mathrm{CO}}$?> , which traces the dense molecular gas fraction, is greater in the two nuclei ( <?CDATA ${L}_{\mathrm{HCN}}/{L}_{\mathrm{CO}}$?> <?CDATA $\sim \quad 0.07-0.08$?> ) than in the overlap region ( <?CDATA ${L}_{\mathrm{HCN}}/{L}_{\mathrm{CO}}$?> <?CDATA $\lt 0.05$?> ). We attribute this to an increase in pressure due to the stellar potential within the nuclei; a similar effect to what has been seen previously in the Milky Way and nearby spiral galaxies. Furthermore, the ratio of <?CDATA ${L}_{\mathrm{HNC}}/{L}_{\mathrm{HCN}}$?> <?CDATA $\sim \quad 0.3-0.4$?> does not vary by more than a factor of 1.5 between regions. By comparing our measured ratios to photon dominated region (PDR) models including mechanical heating, we find that the ratio of <?CDATA ${L}_{\mathrm{HNC}}/{L}_{\mathrm{HCN}}$?> is consistent with mechanical heating contributing ≳5%–10% of the PDR surface heating to the total heating budget. Finally, the ratio of <?CDATA ${L}_{\mathrm{HCN}}/{L}_{\mathrm{HCO}+}$?> varies from ∼1 in the nucleus of NGC 4038 down to ∼0.5 in the overlap region. The lower ratio in the overlap region may be due to an increase in the cosmic ray rate from the increased supernova rate within this region.
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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 | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".