The Circumnuclear Molecular Gas in the Seyfert Galaxy NGC 4945
Bibliographic record
Abstract
We have mapped the central region of NGC 4945 in the J = 2 → 1 transition of 12 CO, 13 CO, and C 18 O, as well as the continuum at ~1.3 mm, at an angular resolution of 5'' × 3'' with the Submillimeter Array. The relative proximity of NGC 4945 (distance of only 3.8 Mpc) permits a detailed study of the circumnuclear molecular gas and dust in a galaxy exhibiting both an active galactic nucleus (AGN; classified as Seyfert 2) and a circumnuclear starburst in an inclined ring with radius ~2.5'' (~50 pc). We infer the systemic velocity ~585 km s -1 from chanel maps and PV-diagrams. We find that all three molecular lines trace an inclined rotating disk with the major axis aligned with that of the starburst ring and large-scale galactic disk and which exhibits solid-body rotation within a radius of ~5'' (~95 pc). The rotation curve flattens beyond this radius, and the isovelocity contours exhibit an S-shaped asymmetry suggestive of a highly inclined bar, as has been invoked to produce a similar asymmetry observed on larger scales. We infer an inclination for the nuclear disk of 62° ± 2°, somewhat smaller than the inclination of the large-scale galactic disk of ~78°. The continuum emission at 1.3 mm also extends beyond the starburst ring and is dominated by thermal emission from dust. If it traces the same dust emitting in the far-infrared, then the bulk of this dust must be heated by star-formation activity rather than the AGN. We discover a kinematically decoupled component at the center of the disk with a radius smaller than 1.4'' (27 pc), but which spans approximately the same range of velocities as the surrounding disk. This component has a higher density than its surroundings and is a promising candidate for the circumnuclear molecular torus invoked by AGN unification models.
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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 | 0.000 | 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) | 0.001 | 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".