<i>HERSCHEL</i>-SPIRE FOURIER TRANSFORM SPECTROMETER OBSERVATIONS OF EXCITED CO AND [C I] IN THE ANTENNAE (NGC 4038/39): WARM AND COLD MOLECULAR GAS
Bibliographic record
Abstract
We present Herschel Spectral and Photometric Imaging Receiver (SPIRE) Fourier Transform Spectrometer (FTS) observations of the Antennae (NGC 4038/39), a well-studied, nearby (22 Mpc), ongoing merger between two gas-rich spiral galaxies. The SPIRE-FTS is a low spatial ( FWHM ∼ 19''–43'') and spectral (∼1.2 GHz) resolution mapping spectrometer covering a large spectral range (194–671 μm, 450–1545 GHz). We detect five CO transitions ( J = 4–3 to J = 8–7), both [C i ] transitions, and the [N ii ] 205 μ m transition across the entire system, which we supplement with ground-based observations of the CO J = 1–0, J = 2–1, and J = 3–2 transitions and Herschel Photodetecting Array Camera and Spectrometer (PACS) observations of [C ii ] and [O i ] 63 μ m . Using the CO and [C i ] transitions, we perform both a local thermodynamic equilibrium (LTE) analysis of [C i ] and a non-LTE radiative transfer analysis of CO and [C i ] using the radiative transfer code RADEX along with a Bayesian likelihood analysis. We find that there are two components to the molecular gas: a cold ( T kin ∼ 10–30 K) and a warm ( T kin ≳ 100 K) component. By comparing the warm gas mass to previously observed values, we determine a CO abundance in the warm gas of x CO ∼ 5 × 10 −5 . If the CO abundance is the same in the warm and cold gas phases, this abundance corresponds to a CO J = 1–0 luminosity-to-mass conversion factor of α CO ∼ 7 M ☉ pc −2 (K km s −1 ) −1 in the cold component, similar to the value for normal spiral galaxies. We estimate the cooling from H 2 , [C ii ], CO, and [O i ] 63 μ m to be ∼0.01 L ☉ / M ☉ . We compare photon-dominated region models to the ratio of the flux of various CO transitions, along with the ratio of the CO flux to the far-infrared flux in NGC 4038, NGC 4039, and the overlap region. We find that the densities recovered from our non-LTE analysis are consistent with a background far-ultraviolet field of strength G 0 ∼ 1000. Finally, we find that a combination of turbulent heating, due to the ongoing merger, and supernova and stellar winds are sufficient to heat the molecular gas.
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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 | 0.002 | 0.001 |
| 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) | 0.004 | 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".