Bending and breathing modes of the Galactic disc
Bibliographic record
Abstract
We explore the hypothesis that a passing satellite or dark matter subhalo has excited coherent oscillations of the Milky Way's stellar disc in the direction perpendicular to the Galactic mid-plane. This work is motivated by recent observations of spatially dependent bulk vertical motions within ∼2 kpc of the Sun. A satellite can transfer a fraction of its orbital energy to the disc stars as it plunges through the Galactic mid-plane, thereby heating and thickening the disc. Bulk motions arise during the early stages of such an event when the disc is still in an unrelaxed state. We present simple toy-model calculations and simulations of disc–satellite interactions, which show that the response of the disc depends on the relative velocity of the satellite. When the component of the satellite's velocity perpendicular to the disc is small compared with that of the stars, the perturbation is pre-dominantly a bending mode. Conversely, breathing and higher order modes are excited when the vertical velocity of the satellite is larger than that of the stars. We argue that the compression and rarefaction motions seen in three different surveys are in fact breathing-mode perturbations of the Galactic disc.
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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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 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".