Purveyors of fine halos: Re-assessing globular cluster contributions to the Milky Way halo buildup with SDSS-IV
Bibliographic record
Abstract
There is ample evidence in the Milky Way for globular cluster (GC) disruption. It may therefore be expected that part of the Galactic halo field star population may also once have formed in GCs. We seek to quantify the fraction of halo stars donated by GCs by searching for stars that bear the unique chemical fingerprints typical for a subset of GC stars often dubbed “second-generation stars”. These are stars showing light-element abundance anomalies such as a pronounced CN-band strength accompanied by weak CH-bands. Based on this indicator, past studies have placed the fraction of halo stars with a GC origin between a few to up to 50%. Using low-resolution spectra from the most recent data release (DR14) of the latest extension of the Sloan Digital Sky Survey (SDSS-IV), we were able to identify 118 metal-poor (−1.8 ≤ [Fe/H] ≤ −1.3) CN-strong stars in a sample of 4470 halo giant stars out to ∼50 kpc. This increases the number of known halo stars with GC-like light-element abundances by a factor of two and results in an observed fraction of these stars of 2.6 ± 0.2%. Using an updated formalism to account for the fraction of stars lost early on in the GC evolution, we thus estimate the fraction of the Galactic halo that stems from disrupted clusters to be very low, at 11 ± 1%. This number would represent the case that stars lost from GCs were entirely from the first generation and is thus merely an upper limit. Our conclusions are sensitive to our assumptions of the mass lost early on from the first generation formed in the GCs, the ratio of first-to-second generation stars, and other GC parameters. We carefully tested the influence of varying these parameters on the final result and find that under realistic scenarios, this fraction depends on the main assumptions at less than 10 percentage points. We further recover a flat trend in this fraction with Galactocentric radius, with a marginal indication of a rise beyond 30 kpc that could reflect the ex situ origin of the outer halo as is also seen in other stellar tracers.
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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) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| 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".