A resolved analysis of cold dust and gas in the nearby edge-on spiral NGC 891
Bibliographic record
Abstract
We investigate the connection between dust and gas in the nearby edge-on spiral galaxy NGC 891, a target of the Very Nearby Galaxies Survey. High resolution Herschel PACS and SPIRE 70, 100, 160, 250, 350, and 500 μm images are combined with JCMT SCUBA 850 μm observations to trace the far-infrared/submillimetre spectral energy distribution (SED). Maps of the Hi 21 cm line and CO(J = 3−2) emission trace the atomic and molecular hydrogen gas, respectively. We fit one-component modified blackbody models to the integrated SED, finding a global dust mass of (8.5 ± 2.0) × 107 M⊙ and an average temperature of 23 ± 2 K, consistent with results from previous far-infrared experiments. We also fit one-component modified blackbody models to pixel-by-pixel SEDs to produce maps of the dust mass and temperature. The dust mass distribution correlates with the total stellar population as traced by the 3.6 μm emission. The derived dust temperature, which ranges from approximately 17 to 24 K, is found to correlate with the 24 μm emission. Allowing the dust emissivity index to vary, we find an average value of β = 1.9 ± 0.3. We confirm an inverse relation between the dust emissivity spectral index and dust temperature, but do not observe any variation of this relationship with vertical height from the mid-plane of the disc. A comparison of the dust properties with the gaseous components of the ISM reveals strong spatial correlations between the surface mass densities of dust (Σdust) and the molecular hydrogen (ΣH2) and total gas surface densities (Σgas). These observations reveal the presence of regions of dense, cold dust that are coincident with peaks in the gas distribution and are associated with a molecular ring. Furthermore, the observed asymmetries in the dust temperature, the H2-to-dust ratio and the total gas-to-dust ratio hint that an enhancement in the star formation rate may be the result of larger quantities of molecular gas available to fuel star formation in the NE compared to the SW. Whilst the asymmetry likely arises from dust obscuration due to the geometry of the line-of-sight projection of the spiral arms, we cannot exclude that there is also an enhancement in the star formation rate in the NE part of the disc.
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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".