The FENIKS Survey: Spectroscopic Confirmation of Massive Quiescent Galaxies at <i>z</i> > 3
Bibliographic record
Abstract
Abstract We report spectroscopic confirmation of a z = 3.757 ± 0.0011 massive $({\rm{log}}({{\rm{M}}_*}/{M_ \odot }) = 10.86_{ - 0.03}^{ + 0.09})$ quiescent galaxy with 11 hours of Keck/MOSFIRE K -band observations. This galaxy was selected from the FENIKS survey, which uses deep Gemini/ Flamingos-2 K b K r imaging optimized for increased sensitivity to galaxies with strong Balmer/4000 Å breaks. Its rest-frame colors are consistent with a ∼1 Gyr old stellar population. This places it as one of the oldest objects at these redshifts, and challenges the notion that quiescent galaxies at z > 3 are all young post-starbursts. The star formation history suggests that its progenitor was in place by z ∼4 −7, reaching 10 10.6 M ȯ by z ∼ 5, which we have confirmed using ultra-deep medium resolution spectroscopy from JWST . These results are in line with the rapid formation and quenching timescales reported for similar massive quiescent galaxies at z > 3, implying extreme baryonic physics within the first billion years of cosmic history.
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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 | 0.000 |
| Science and technology studies | 0.001 | 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) | 0.002 | 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".