A large population of recently quenched red-sequence dwarf galaxies in the outskirts of the Coma cluster
Bibliographic record
Abstract
Abstract We analyse the stellar populations of 75 red-sequence dwarf galaxies in the Coma cluster, based on high signal-to-noise ratio spectroscopy from the 6.5-m MMT. The sample covers a luminosity range 3–4 mag below M★, in the cluster core and in a field centred 1° to the south-west. We find a strong dependence of the absorption-line strengths with location in the cluster. Galaxies further from the cluster centre have stronger Balmer lines than inner-field galaxies of the same luminosity. The magnesium lines are weaker at large radius, while the iron lines are not correlated with radius. Converting the line strengths into estimates of stellar age, metallicity and abundance ratios, we find the gradients are driven by variations in age (>6σ significance) and in the iron abundance Fe/H (∼2.7σ significance). The light element (Mg, C, N, Ca) abundances are almost independent of radius. At radius of times the virial radius), dwarf galaxies have ages ∼3.8 Gyr on average, compared to ∼6 Gyr near the cluster centre. The outer dwarfs are also ∼50 per cent more iron-enriched, at given luminosity. Our results confirm earlier indications that the ages of red-sequence galaxies depend on location within clusters, and in Coma in particular. The very strong trends found here suggest that dwarf galaxies are especially susceptible to environmental ‘quenching’, and/or that the south-west part of Coma is particularly a clear example of recent quenching in an infalling subcluster.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".