The Dawn of the Red: star formation histories of group galaxies over the past 5 billion years
Bibliographic record
Abstract
We examine the star formation properties of group and field galaxies in two surveys, Sloan Digital Sky Survey (at z∼ 0.08) and Group Environment Evolution Collaboration (GEEC; at z∼ 0.4). Using ultraviolet imaging from the Galaxy Evolution Explorer space telescope, along with optical and, for GEEC, near-infrared photometry, we compare the observed spectral energy distributions to large suites of stellar population synthesis models. This allows us to accurately determine star formation rates and stellar masses. We find that star-forming galaxies of all environments undergo a systematic lowering of their star formation rate between z= 0.4 and 0.08 regardless of mass. None the less, the fraction of passive galaxies is higher in groups than the field at both redshifts. Moreover, the difference between the group and field grows with time and is mass dependent, in the sense the difference is larger at low masses. However, the star formation properties of star-forming galaxies, as measured by their average specific star formation rates, are consistent within the errors in the group and field environment at fixed redshift. The evolution of passive fraction in groups between z= 0.4 and 0 is consistent with a simple accretion model, in which galaxies are environmentally affected 3 Gyr after falling into a ∼1013 M⊙ group. This long time-scale appears to be inconsistent with the need to transform galaxies quickly enough to ensure that star-forming galaxies appear similar in both the group and field, as observed.
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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 | 0.000 | 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 | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| 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".