DUST ABUNDANCE AND PROPERTIES IN THE NEARBY DWARF GALAXIES NGC 147 AND NGC 185
Bibliographic record
Abstract
We present new mid- to far-infrared images of the two dwarf compact elliptical galaxies that are satellites of M31, NGC 185, and NGC 147, obtained with the Spitzer Space Telescope . Spitzer 's high sensitivity and spatial resolution enable us for the first time to look directly into the detailed spatial structure and properties of the dust in these systems. The images of NGC 185 at 8 and 24 μm display a mixed morphology characterized by a shell-like diffuse emission region surrounding a central concentration of more intense infrared emission. The lower resolution images at longer wavelengths show the same spatial distribution within the central 50'' but beyond this radius, the 160 μm emission is more extended than that at 24 and 70 μm. On the other hand, the dwarf galaxy NGC 147, located only a small distance away from NGC 185, shows no significant infrared emission beyond 24 μm and therefore its diffuse infrared emission is mainly stellar in origin. For NGC 185, the derived dust mass based on the best fit to the spectral energy distribution is 1.9 × 10 3 M ☉ , implying a gas mass of 3.0 × 10 5 M ☉ . These values are in agreement with those previously estimated from infrared as well as CO and H i observations and are consistent with the predicted mass return from dying stars based on the last burst of star formation 1 × 10 9 yr ago. Based on the 70–160 μm flux density ratio, we estimate a temperature for the dust of ∼17 K. For NGC 147, we obtain an upper limit for the dust mass of 4.5 × 10 2 M ☉ at 160 μm (assuming a temperature of ∼20 K), a value consistent with the previous upper limit derived using Infrared Space Observatory observations of this galaxy. In the case of NGC 185, we also present full 5–38 μm low-resolution ( R ∼ 100) spectra of the main emission regions. The Infrared Spectrograph spectra of NGC 185 show strong polycyclic aromatic hydrocarbons emission, deep silicate absorption features and H 2 pure rotational line ratios consistent with having the dust and molecular gas inside the dust cloud being impinged by the far-ultraviolet radiation field of a relatively young stellar population. Therefore, based on its infrared spectral properties, NGC 185 shows signatures of recent star formation (a few × 10 8 yr ago), although its current star formation rate is quite low.
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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) | 0.000 | 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".