Nitrogen Abundance Distribution in the Inner Milky Way
Bibliographic record
Abstract
Abstract We combine a new Galactic plane survey of hydrogen radio recombination lines (RRLs) with far-infrared surveys of ionized nitrogen, N+, to determine nitrogen abundance across Galactic radius. RRLs were observed with the NASA Deep Space Network Station 43 70 m antenna and the Green Bank Telescope in 108 lines of sight spanning −135°< l < 60°, at b = 0°. These positions were also observed in [N ii] 122 μm and 205 μm lines with the Herschel Space Observatory. Combining RRL and [N ii] 122 μm and 205 μm observations in 41 of 108 samples with high signal-to-noise ratio, we studied the ionized nitrogen abundance distribution across Galactocentric distances of 0–8 kpc. Combined with existing solar neighborhood and outer Galaxy N/H abundance determinations, we studied this quantity’s distribution within the Milky Way’s inner 17 kpc for the first time. We found a nitrogen abundance gradient extending from Galactocentric radii of 4–17 kpc in the Galactic plane, while within 0–4 kpc the N/H distribution remained flat. The gradient observed at large Galactocentric distances supports inside-out galaxy growth, with the additional steepening resulting from variable star formation efficiency and/or radial flows in the Galactic disk, while the inner 4 kpc flattening, coinciding with the Galactic bar’s onset, may be linked to radial flows induced by the bar potential. Using SOFIA/FIFI-LS and Herschel/PACS, we observed the [N iii] 57 μm line to trace doubly ionized gas contribution in a subsample of sight lines. We found negligible N++ contributions along these sight lines, suggesting mostly singly ionized nitrogen originating from low-ionization H ii region outskirts.
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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 | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".