Obscured star formation in clusters at <i>z</i> = 1.6–2.0: massive galaxy formation and the reversal of the star formation–density relation
Bibliographic record
Abstract
ABSTRACT Clusters of galaxies at z $\mathrel {\gtrsim }$ 1 are expected to be increasingly active sites of star formation. To test this, an 850 $\mu$m survey was undertaken of eight clusters at z = 1.6–2.0 using SCUBA-2 on the James Clerk Maxwell Telescope. Mid-infrared properties were used to identify 53 probable counterparts to 45 SCUBA-2 sources with colours that suggested they were cluster members. This uncovered a modest overdensity of 850 $\mu$m sources, with far-infrared luminosities of LIR ≥ 1012 L⊙ (SFR $\mathrel {\gtrsim }$ 100 M⊙ yr−1) and colours consistent with being cluster members, of a factor of 4 ± 1 within the central 1 Mpc radius of the clusters. The submillimetre photometry of these galaxies was used to estimate the total cluster star formation rates. These showed that the mass-normalized rates in the clusters are two orders of magnitude higher than in local systems, evolving as (1 + z)5.5 ± 0.6. This rapid evolution means that the mass-normalized star formation rates in these clusters matched that of average haloes in the field at z ∼ 1.8 ± 0.2 marking the epoch where the local star formation–density relation reverses in massive haloes. The estimated stellar masses of the cluster submillimetre galaxies suggests that their descendants will be amongst the most massive galaxies in z ∼ 0 clusters. This reinforces the suggestion that the majority of the massive early-type galaxy population in z ∼ 0 clusters were likely to have formed at z $\mathrel {\gtrsim }$ 1.5–2 through very active, but dust-obscured, starburst events.
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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 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".