Near-infrared imaging of 222 nearby H -strong galaxies from the Sloan Digital Sky Survey
Bibliographic record
Abstract
We present UFTI K-band imaging observations of 222 galaxies that are selected from the Sloan Digital Sky Survey to have unusually strong Hδ absorption equivalent widths, W○(Hδ) > 4 Å. Using gim2d, the images are fitted with two-dimensional surface-brightness models consisting of a simple disc and bulge component to derive the fraction of luminosity in the bulge B/T. We find that the galaxies with weak or absent Hα or [Oii]λ3727 emission (known as k+a galaxies) are predominantly bulge-dominated (with a mode of B/T∼ 0.6), while galaxies with nebular emission [known as e(a) galaxies] are mostly disc-dominated (B/T∼ 0.1). The morphologies and (r−k) colours of most k+a galaxies are inconsistent with the hypothesis that they result from the truncation of star formation in normal, spiral galaxies. However, their (u−g) and (r−k) colours, as well as their Hδ line strengths, form a sequence that is well matched by a model in which >5 per cent of the stellar mass has been produced in a recent starburst. The lack of scatter in the dust-sensitive (r−k) colours suggests that the unusual spectra of k+a galaxies are not due to the effects of dust. The e(a) galaxies, on the other hand, have a colour distribution that is distinct from the k+a population, and typical of normal or dusty (τV∼ 2) spiral galaxies. We conclude that many e(a) galaxies are not progenitors of k+a galaxies, but are a separate phenomenon. Both k+a and e(a) galaxies reside in environments (characterized by the local density of galaxies brighter than Mr=−20) that are typical of normal galaxies and that are inconsistent with overdense regions like rich galaxy clusters.
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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 | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 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".