Globular cluster systems in nearby dwarf galaxies - II. Nuclear star clusters and their relation to massive Galactic globular clusters
Bibliographic record
Abstract
We compare nuclear globular clusters (nGCs) in dwarf galaxies and Galactic GCs with extended (hot) horizontal branches (EHB-GCs) in order to test the suggested external origin of the latter and the conditions at which GC self-enrichment can operate. Using luminosities and structural parameters of nGCs in low-mass (mainly late-type) dwarf galaxies from Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) imaging, we derive the present-day escape velocities (υesc) of stellar ejecta to reach the cluster tidal radius and compare them with those of EHB-GCs. We show that nGCs in dwarf galaxies are very similar in their photometric and structural properties (colour 〈V−I〉= 0.9 mag, magnitudes 〈MV〉 < −9 mag, ellipticities 〈ε〉= 0.11) to EHB-GCs. The nGCs populate the same MV versus rh region as EHB-GCs, although they do not reach the sizes of the largest EHB-GCs like ω Cen and NGC 2419. We suggest that during accretion the rh of an nGC could increase due to significant mass loss in the cluster vicinity and the resulting drop in the external potential in the core once the dwarf galaxy dissolves. For EHB-GCs, we find a correlation between the present-day υesc and their metallicity as well as (V−I)0 colour. The similar υesc, (V−I)0 distribution of nGCs and EHB-GCs imply that nGCs could also have complex stellar populations. The υesc–[Fe/H] relation could reflect the known relation of increasing stellar wind velocity with metallicity, which in turn could explain why more metal-poor clusters typically show more peculiarities in their stellar population than more metal-rich clusters of the same mass do. Thus, the cluster υesc can be used as a parameter to describe the degree of self-enrichment. All our findings support the scenario in which Galactic EHB-GCs have originated in the centres of pre-Galactic building blocks or dwarf galaxies that were later accreted by the Milky Way.
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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 | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".