Cosmic Pathways for Compact Groups in the Milli-Millennium Simulation
Bibliographic record
Abstract
Abstract We detected 10 compact galaxy groups (CGs) at z = 0 in the semianalytic galaxy catalog of Guo et al. for the milli-Millennium Cosmological Simulation (sCGs in mGuo2010a). We aimed to identify potential canonical pathways for compact group evolution and thus illuminate the history of observed nearby CGs. By constructing merger trees for z = 0 sCG galaxies, we studied the cosmological evolution of key properties and compared them with z = 0 Hickson CGs (HCGs). We found that, once sCG galaxies come within 1 (0.5) Mpc of their most massive galaxy, they remain within that distance until z = 0, suggesting sCG “birth redshifts.” At z = 0 stellar masses of sCG most massive galaxies are within 1010 ≲ M */M ⊙ ≲ 1011. In several cases, especially in the two four- and five-member systems, the amount of cold gas mass anticorrelates with stellar mass, which in turn correlates with hot gas mass. We define the angular difference between group members’ 3D velocity vectors, Δθ vel, and note that many of the groups are long-lived because their small values of Δθ vel indicate a significant parallel component. For triplets in particular, Δθ vel values range between 20° and 40° so that galaxies are coming together along roughly parallel paths, and pairwise separations do not show large pronounced changes after close encounters. The best agreement between sCG and HCG physical properties is for M * galaxy values, but HCG values are higher overall, including for star formation rates (SFRs). Unlike HCGs, due to a tail at low SFR and M * and a lack of M * ≳ 1011 M ⊙ galaxies, only a few sCG galaxies are on the star-forming main sequence.
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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 | 0.001 | 0.003 |
| 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 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".