GSH 138−01−94: An Old Supernova Remnant in the Far Outer Galaxy
Bibliographic record
Abstract
The properties of the Galactic H I shell GSH 138-01-94 are derived from data of the Canadian Galactic Plane Survey. The basic parameters of GSH 138-01-94 were determined by fitting the expansion of a thin shell to the expansion velocity field on the sky. The kinematic distance is 16.6 kpc for v LSR = -94.2 ± 0.5 km s -1 . The radius is 180 ± 10 pc, the expansion velocity v exp = 11.8 ± 0.9 km s -1 , and the mass 2 × 10 5 M ☉ . No radio-continuum counterpart of the shell was detected at 21 cm or at 74 cm. Absorption of a background continuum source constrains the spin temperature of H I in the shell to T s = 230 K. The expansion age of GSH 138-01-94 is 4.3 Myr. These observables are in excellent agreement with predictions from hydrodynamic models for a supernova remnant in a low-density, low-metallicity environment such as the outer Galaxy. GSH 138-01-94 is then the largest and the oldest supernova remnant known. It provides direct evidence for the release of mechanical energy in the interstellar medium by stars in the outer Galaxy. We argue that such old supernova remnants are to be found in low-density, low-metallicity environments such as the outer Galaxy, dwarf galaxies, and low surface brightness galaxies.
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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 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".