Unveiling the Cosmic Gems Arc at <i>z</i> ∼ 10 with JWST NIRCam
Bibliographic record
Abstract
Abstract We present recent JWST NIRCam imaging observations of SPT0615-JD (also known as the Cosmic Gems Arc), lensed by the galaxy cluster SPT-CL J0615−5746. The 5″ long arc is the most highly magnified z > 10 galaxy known. It straddles the lensing critical curve and reveals five star clusters with radii of ∼1 pc or less. We measure the full arc to have F200W 24.5 AB mag, consisting of two mirror images, each 25.3 AB mag with a median magnification of μ ∼ 6 0 − 8 + 17 (delensed 29.7 AB mag, M UV = −17.8). The galaxy has an extremely strong Lyman break F115W−F200W >3.2 mag (2σ lower limit), is undetected in all bluer filters (<2σ), and has a very blue continuum slope redward of the break (β = −2.7 ± 0.1). This results in a photometric redshift z phot = 10.2 ± 0.2 (95% confidence) with no significant likelihood below z < 9.8. Based on spectral energy distribution fitting to the total photometry, we estimate an intrinsic stellar mass of M * ∼ 2.4–5.6 × 107 M ⊙, young mass-weighted age of ∼21–79 Myr, low dust content (A V < 0.15), and a low metallicity of ≲1% Z ⊙. We identify a fainter third counterimage candidate within 2 . ″ 2 of the predicted position, lensed to AB mag 28.4 and magnified by μ ∼ 2, suggesting the fold arc may only show ∼60% of the galaxy. SPT0615-JD is a unique laboratory to study star clusters observed within a galaxy just 460 Myr after the Big Bang.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 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".