A multi-wavelength overview of the giant spiral UGC 2885
Bibliographic record
Abstract
\nContext. UGC 2885 (z = 0.01935) is one of the largest and most massive galaxies in the local Universe, yet it has an undisturbed spiral structure, which is unexpected for such an object and is not predicted by cosmological simulations. Understanding the detailed properties of extreme systems such as UGC 2885 can provide insight into the limits of scaling relations and the physical processes driving galaxy evolution.\nAims. Our goal is to understand whether UGC 2885 has followed a similar evolutionary path as other high-mass galaxies by examining its place in the fundamental metallicity relation and on the star-forming main sequence.\nMethods. We present new observations of UGC 2885 with the Canada-France-Hawaii Telescope and the Institut de radioastronomie millimétrique 30 m telescope. We used these novel data to calculate metallicity and molecular hydrogen mass values, respectively. We estimated the stellar mass (M⋆) and star formation rate (SFR) based on mid-infrared observations with the Wide-field Infrared Survey Explorer.\nResults. We find global metallicities Z = 9.28, 9.08, and 8.74 at the 25 kpc ellipsoid from the N2O2, R23, and O3N2 indices, respectively. This puts UGC 2885 at the high end of the galaxy metallicity distribution. We find a molecular hydrogen mass of MH2 = 1.89 ± 0.24 × 1011 M⊙, a SFR of 1.63 ± 0.72 M⊙ yr−1, and a stellar mass of 4.83 ± 1.52 × 1011 M⊙, which gives a star formation efficiency (SFR/MH2) of 8.67 ± 4.20 × 1012 yr−1. This indicates that UGC 2885 has an extremely high molecular gas content compared to known samples of star-forming galaxies (∼100 times more) and a relatively low SFR for its current gas content.\nConclusions. We conclude that UGC 2885 has gone through cycles of star formation periods, which increased its stellar mass and metallicity to its current state. The mechanisms that are fuelling the current molecular gas reservoir and keeping the galaxy from producing stars remain uncertain. We discuss the possibility that a molecular bar is quenching star-forming activity.\n
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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 | 0.005 | 0.004 |
| Science and technology studies | 0.001 | 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) | 0.005 | 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".