Interstellar Medium Abundances in Sculptor Group Dwarf Irregular Galaxies
Bibliographic record
Abstract
Using the Cerro Tololo Inter-American Observatory 4 m telescope, we have obtained optical spectra of H II regions in five Sculptor group dwarf irregular galaxies. We derive oxygen, nitrogen, and sulfur abundances from the H II region spectra. Oxygen abundances are derived via three different methods (the "direct" method, the empirical method guided by photoionization modeling of McGaugh [published in 1991], and the purely empirical method of Pilyugin, published in 2000) and are compared. Significant systematic differences are found between the three methods, and we suggest that a recalibration of the empirical abundance scale is required. Until differences between these three methods are better understood, the issue of the degree of uniformity of the interstellar medium abundances in a dwarf galaxy cannot be properly addressed. The N/O ratio for the metal-poor dI ESO 473-G24 of log (N/O) = -1.43 ± 0.03 lies well above the plateau of log (N/O) = -1.60 ± 0.02 found by Izotov & Thuan for a collection of metal-poor, blue compact galaxies. This shows that not all galaxies with 12 + log (O/H) ≤ 7.6 have identical elemental abundance ratios, and this implies that the Izotov & Thuan scenario for low-metallicity galaxies is not universal. Measurements of the H II regions in NGC 625 yield log (N/O) ≈ -1.25. Assuming N production by intermediate-mass stars, this relatively high N/O ratio may be indicative of a long quiescent period prior to the recent active burst of star formation. The oxygen abundances in the Sculptor group dI's are in good agreement with the relationship between metallicity and luminosity observed in the Local Group dI's. Taken together, the observations show a better relationship between metallicity and luminosity than between metallicity and galaxy central surface brightness. The Sculptor group dI's, in general, lie closer to the simple closed-box model evolutionary path than the Local Group dI's. The higher gas contents, lower average star formation rates, and closer resemblance to closed-box evolution could all be indicative of evolution in a relatively low density environment.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.005 | 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".