Evolved Galaxies at <i>z</i> > 1.5 from the Gemini Deep Deep Survey: The Formation Epoch of Massive Stellar Systems
Bibliographic record
Abstract
We present spectroscopic evidence from the Gemini Deep Deep Survey for a significant population of color-selected red galaxies at 1.3 < z, < 2.2 whose integrated light is dominated by evolved stars. Unlike radio-selected objects, the z > 1.5 old galaxies have a sky density greater than 0.1 arcmin-2. Conservative age estimates for 20 galaxies with z > 1.3. 〈z〉 = 1.49, give a median age of 1.2 Gyr and 〈z f〉 = 2.4. One-quarter of the galaxies have inferred z f > 4. Models restricted to [Fe/H[ ≤ 0 give median ages and zf of 2.3 Gyr and 3.3, respectively. These galaxies are among the most massive and contribute ∼50% of the stellar mass density at 1 < z < 2. The derived ages and most probable star formation histories suggest a high star formation rate (∼300-500 M⊙, yr-1) phase in the progenitor population. We argue that most of the red galaxies are not descendants of the typical z ∼ 3 Lyman break galaxies. Galaxies associated with luminous submillimeter sources have the requisite star formation rates to be the progenitor population. Our results point toward early and rapid formation for a significant fraction of present-day massive galaxies.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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 teacher head, 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".