THE NUCLEUS OF THE SAGITTARIUS DSPH GALAXY AND M54: A WINDOW ON THE PROCESS OF GALAXY NUCLEATION
Bibliographic record
Abstract
We present the results of a thorough study of the nucleus of the Sgr dwarf spheroidal galaxy (Sgr dSph) and of the bright globular cluster M54 (NGC 6715) that resides within the same nucleus (Sgr,N). We have obtained accurate radial velocities and metallicity estimates for 1152 candidate red giant branch stars of Sgr and M54 lying within ∼9' from the center of the galaxy, from Keck/DEIMOS and VLT/FLAMES spectra of the infrared Ca ii triplet. Using both velocity and metallicity information we selected two samples of 425 and 321 very likely members of M54 and of Sgr,N, respectively. The two considered systems display significantly different velocity dispersion profiles. M54 has a steeply decreasing profile from r = 0', where σ ≃ 14.2 km s −1 , to r ≃ 3 5 where it reaches σ ≃ 5.3 km s −1 , then it appears to rise again to σ ≃ 10 km s −1 at r ∼ 7'. In contrast Sgr,N has a uniformly flat profile at σ ≃ 9.6 km s −1 over the whole 0' ⩽ r ⩽ 9' range. Using data from the literature we show that the velocity dispersion of Sgr remains constant at least out to r ∼ 100' and there is no sign of the transition between the outer flat-luminosity-profile core and the inner nucleus in the velocity profile. These results, together with a re-analysis of the surface brightness profile of Sgr,N and a suite of dedicated N -body simulations, provide very strong support for the hypothesis that the nucleus of Sgr formed independently of M54, which probably plunged to its present position, coincident with Sgr,N, because of significant decay of the original orbit due to dynamical friction.
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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 | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".