Still Missing Dark Matter: KCWI High-resolution Stellar Kinematics of NGC1052-DF2
Bibliographic record
Abstract
Abstract The velocity dispersion of the ultra diffuse galaxy NGC1052-DF2 was found to be km s −1 , much lower than expected from the stellar mass–halo mass relation and nearly identical to the expected value from the stellar mass alone. This result was based on the radial velocities of 10 luminous globular clusters that were assumed to be associated with the galaxy. A more precise measurement is possible from high-resolution spectroscopy of the diffuse stellar light. Here we present an integrated spectrum of the diffuse light of NGC1052-DF2 obtained with the Keck Cosmic Web Imager (KCWI), with an instrumental resolution of σ instr ≈ 12 km s −1 . The systemic velocity of the galaxy is v sys = 1805 ± 1.1 km s −1 , in very good agreement with the average velocity of the globular clusters ( km s −1 ). There is no evidence for rotation within the KCWI field of view. We find a stellar velocity dispersion of km s −1 , consistent with the dispersion that was derived from the globular clusters. The implied dynamical mass within the half-light radius r 1/2 = 2.7 kpc is M dyn = (1.3 ± 0.8) × 10 8 M ⊙ , similar to the stellar mass within that radius ( M stars = (1.0 ± 0.2) × 10 8 M ⊙ ). With this confirmation of the low velocity dispersion of NGC1052-DF2, the most urgent question is whether this “missing dark matter problem” is unique to this galaxy or applies more widely.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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) | 0.000 | 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) | 0.000 | 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".