Broadband Optical Properties of Massive Galaxies: The Dispersion around the Field Galaxy Color-Magnitude Relation Out to<i>z</i> ~ 0.4
Bibliographic record
Abstract
Using a sample of nearly 20,000 massive early-type galaxies selected from the Sloan Digital Sky Survey, we study the color-magnitude relation for the most luminous ( L ≳ 2.2 L *) field galaxies in the redshift range 0.1 < z < 0.4 in several colors. The intrinsic dispersion in galaxy colors is quite small in all colors studied, but the 40 millimag (mmag) scatter in the bluest colors is a factor of 2 larger than the 20 mmag measured in the reddest bands. While each of three simple models constructed for the star formation history in these systems can satisfy the constraints placed by our measurements, none of them produce color distributions matching those observed. Subdividing by environment, we find the dispersion for galaxies in clusters to be about 11% smaller than that of more isolated systems. Finally, having resolved the red sequence, we study the color dependence of the composite spectra. Bluer galaxies on the red sequence are found to have more young stars than red galaxies; the extent of this spectral difference is marginally better described by passive evolution of an old stellar population than by a model consisting of a recent trace injection of young stars.
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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 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.003 | 0.001 |
| Science and technology studies | 0.000 | 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 | 0.001 |
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".