Stellar chemo-kinematics of the Cetus dwarf spheroidal galaxy
Bibliographic record
Abstract
Context. The great majority of early-type dwarf galaxies, in the Local Group as well as in other galaxy groups, are found in the vicinity of much larger galaxies, making it hard to disentangle the role of internal versus external effects in driving their evolution. Aims. In order to minimize environmental effects and gain an insight into the internal mechanisms that shape the properties of these systems, we study one of the few dwarf spheroidal galaxies of the Local Group found in isolation: Cetus. This system is of particular interest since it does not follow the Local Group morphology-density relation. Methods. We obtained Very Large Telescope (VLT) FORS2 spectra (R ∼ 2600) in the region of the nIR CaII triplet lines for 80 candidate red giant branch (RGB) stars. The analysis yielded line-of-sight velocities and metallicities ([Fe/H]) for 54 bona fide member stars. Results. The kinematic analysis shows that Cetus is a mainly pressure-supported $ ({{\sigma}_{v}}=110_{-1.3}^{+1.6}{\text{km}} {{\text{s}}^{-1}})$, dark-matter-dominated system ($ M_{1/2}/L_V = 23.9_{-8.9}^{+9.7}\,M_\odot/L_\odot $) with no significant signs of internal rotation. We find Cetus to be a metal-poor system with a significant metallicity spread (median [Fe/H]= − 1.71 dex, median-absolute-deviation = 0.49 dex), as expected for its stellar mass. We report the presence of a mild metallicity gradient compatible with those found in other dwarf spheroidals of the same luminosity; we trace the presence of a stellar population gradient also in the spatial distribution of stars in different evolutionary phases in ancillary SuprimeCam photometric data. There are tentative indications of two chemo-kinematically distinct sub-populations, with the more metal-poor stars showing a hotter kinematics than the metal-richer ones. Furthermore, the photometric dataset reveals the presence of a foreground population that most likely belongs to the Sagittarius stream. Conclusions. This study represents an important step forward in assessing the internal kinematics of the Cetus dwarf spheroidal galaxy as well as the first wide-area spectroscopic determination of its metallicity properties. With our analysis, Cetus adds to the growing scatter in stellar-dark matter halo properties in low-mass galactic systems. The presence of a metallicity gradient akin to those found in similarly luminous and pressure-supported systems inhabiting very different environments may hint at metallicity gradients in Local Group early-type dwarfs being driven by internal mechanisms.
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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 | 0.000 |
| 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) | 0.001 | 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".