M31’s Undisturbed Thin Disk of Globular Clusters
Bibliographic record
Abstract
We show that there is a subsystem of the M31 globular clusters with thin-disk kinematics. These clusters span the entire metallicity range of the M31 globular cluster system, in contrast to the (thick) disk globular clusters in the Milky Way, which are predominantly metal-rich. Disk globular clusters are found across the entire disk of M31 and form ~40% of the clusters projected on its disk. The existence of such a disk system suggests that there was a relatively large thin disk in place very early in M31's history. Accurate measures of the ages of these clusters will constrain the epoch of disk formation in M31. There is currently no strong evidence for differences in age between Milky Way and M31 globular clusters. While age differences are subtle for old populations, it is unlikely that disk clusters with [Fe/H] around -2.0 were formed after significant star formation began in the galaxy, as the protocluster gas would be enriched by supernova ejecta. Thus it is likely that M31 had a rather large disk in place at early epochs. The very existence of such a cold disk means that M31 has suffered no mergers with an object of 10% or more of the disk mass since the clusters were formed. This makes the suggestion of Brown et al. that M31 could have suffered an equal-mass merger 6-8 Gyr ago less viable.
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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 | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| 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".