The Extremely Metal-poor SN 2023ufx: A Local Analog to High-redshift Type II Supernovae
Bibliographic record
Abstract
Abstract We present extensive observations of the Type II supernova (SN II) SN 2023ufx, which is likely the most metal-poor SN II observed to date. It exploded in the outskirts of a low-metallicity (Z host ∼ 0.1 Z ⊙) dwarf (M g = −13.39 ± 0.16 mag, r proj ∼ 1 kpc) galaxy. The explosion is luminous, peaking at M g ≈ −18.5 mag, and shows rapid evolution. The r-band (pseudobolometric) light curve has a shock-cooling phase lasting 20 (17) days followed by a 19 (23) day plateau. The entire optically thick phase lasts only ≈55 days following explosion, indicating that the red supergiant progenitor had a thinned H envelope prior to explosion. The early spectra obtained during the shock-cooling phase show no evidence for narrow emission features and limit the preexplosion mass-loss rate to M ̇ ≲ 10 − 3 M ⊙ yr−1. The photospheric-phase spectra are devoid of prominent metal absorption features, indicating a progenitor metallicity of ≲0.1 Z ⊙. The seminebular (∼60–130 days) spectra reveal weak Fe ii, but other metal species typically observed at these phases (Ti ii, Sc ii, and Ba ii) are conspicuously absent. The late-phase optical and near-infrared spectra also reveal broad (≈104 km s−1) double-peaked Hα, Pβ, and Pγ emission profiles suggestive of a fast outflow launched during the explosion. Outflows are typically attributed to rapidly rotating progenitors, which also prefer metal-poor environments. This is only the second SN II with ≲0.1 Z ⊙ and both exhibit peculiar evolution, suggesting a sizable fraction of metal-poor SNe II have distinct properties compared to nearby metal-enriched SNe II. These observations lay the groundwork for modeling the metal-poor SNe II expected in the early Universe.
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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) | 0.002 | 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".