Internal Dynamics, Structure, and Formation of Dwarf Elliptical Galaxies. I. A Keck/[ITAL]Hubble Space Telescope[/ITAL] Study of Six Virgo Cluster Dwarf Galaxies
Bibliographic record
Abstract
Spectroscopy with the Keck II 10 m telescope and Echelle Spectrograph and Imager is presented for six Virgo Cluster dwarf elliptical (dE) galaxies in the absolute magnitude range -15.7 ≤ M V ≤ -17.2. The mean line-of-sight velocity and velocity dispersion are resolved as a function of radius along the major axis of each galaxy, nearly doubling the total number of dEs with spatially resolved stellar kinematics. None of the observed objects shows evidence of strong rotation; upper limits on v rot /σ, the ratio of the maximum rotational velocity to the mean velocity dispersion, are well below those expected for rotationally flattened objects. Such limits place strong constraints on dE galaxy formation models. Although these galaxies continue the trend of low rotation velocities observed in Local Group dEs, they are in contrast to recent observations of large rotation velocities in slightly brighter cluster dEs. Using surface photometry from Hubble Space Telescope Wide Field Planetary Camera 2 images and spherically symmetric dynamical models, we determine global mass-to-light ratios 3 ≤ Υ V ≤ 6. These ratios are comparable to those expected for an old to intermediate-age stellar population and are broadly consistent with the observed V-I colors of the galaxies. These dE galaxies therefore do not require a significant dark matter component inside an effective radius. We are able to rule out central black holes more massive than ∼10 7 M ⊙ . For the five nucleated dEs in our sample, kinematic and photometric properties were determined for the central nucleus separately from the underlying host dE galaxy. These nuclei are as bright or brighter than the most luminous Galactic globular clusters and lie near the region of fundamental plane space occupied by globular clusters. In this space, the Virgo dE galaxies lie in the same general region as Local Group and other nearby dEs, although nonrotating dEs appear to have a slightly higher mean mass and mass-to-light ratio than rotating dEs; the dE galaxies occupy a plane parallel to, but offset from, that occupied by normal elliptical galaxies.
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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 | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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".