JADES: Probing interstellar medium conditions at <i>z</i> ∼ 5.5–9.5 with ultra-deep JWST/NIRSpec spectroscopy
Bibliographic record
Abstract
We present emission-line ratios from a sample of 27 Lyman-break galaxies from z ∼ 5.5 − 9.5 with −17.0 < M 1500 < −20.4, measured from ultra-deep JWST/NIRSpec multi-object spectroscopy from the JWST Advanced Deep Extragalactic Survey (JADES). We used a combination of 28 h deep PRISM/CLEAR and 7 h deep G 395 M / F 290 LP observations to measure, or place strong constraints on, ratios of widely studied rest-frame optical emission lines including H α , H β , [O II ] λλ 3726, 3729, [Ne III ] λ 3869, [O III ] λ 4959, [O III ] λ 5007, [O I ] λ 6300, [N II ] λ 6583, and [S II ] λλ 6716, 6731 in individual z > 5.5 spectra. We find that the emission-line ratios exhibited by these z ∼ 5.5 − 9.5 galaxies occupy clearly distinct regions of line-ratio space compared to typical z ∼ 0 − 3 galaxies, instead being more consistent with extreme populations of lower-redshift galaxies. This is best illustrated by the [O III ]/[O II ] ratio, tracing interstellar medium (ISM) ionisation, in which we observe more than half of our sample to have [O III ]/[O II ] > 10. Our high signal-to-noise spectra reveal more than an order of magnitude of scatter in line ratios such as [O II ]/H β and [O III ]/[O II ], indicating significant diversity in the ISM conditions within the sample. We find no convincing detections of [N II ] λ 6583 in our sample, either in individual galaxies, or a stack of all G 395 M / F 290 LP spectra. The emission-line ratios observed in our sample are generally consistent with galaxies with extremely high ionisation parameters (log U ∼ −1.5), and a range of metallicities spanning from ∼0.1 × Z ⊙ to higher than ∼0.3 × Z ⊙ , suggesting we are probing low-metallicity systems undergoing periods of rapid star formation, driving strong radiation fields. These results highlight the value of deep observations in constraining the properties of individual galaxies, and hence probing diversity within galaxy population.
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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 | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| 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".