The structure of massive star-forming galaxies from JWST and ALMA: Dusty, high-redshift disc galaxies
Bibliographic record
Abstract
We present an analysis of the JWST NIRCam and MIRI morphological and structural properties of 80 massive (log 10 ( M * [M ⊙ ]) = 11.2 ± 0.1) dusty star-forming galaxies at z = 2.7 −0.7 +1.2 , identified as sub-millimetre galaxies (SMGs) by ALMA, which have been observed as part of the JWST PRIMER project. To compare the structure of these massive, active galaxies to more typical, less actively star-forming galaxies, we defined two comparison samples. The first of 850 field galaxies matched in specific star formation rate and redshift and the second of 80 field galaxies matched in stellar mass. From the visual classification of the SMGs, we have identified 20 ± 5% as candidate late-stage major mergers, a further 40 ± 10% as potential minor mergers, and 40 ± 10% that have comparatively undisturbed disc-like morphologies, with no obvious massive neighbours on ≲20–30 kpc (projected) scales. These rates are comparable to those for the field samples and indicate that the majority of the sub-millimetre-detected galaxies are not late-stage major mergers, but have interaction rates similar to the general field population at z ∼ 2–3. Through a multi-wavelength morphological analysis, using parametric and non-parametric techniques, we establish that SMGs have comparable near-infrared, mass-normalised sizes to the less active population, R 50 F444W = 2.7 ± 0.2 kpc versus R F444W 50 = 3.1 ± 0.1 kpc, but exhibit lower Sérsic indices, consistent with bulge-less discs: n F444W = 1.1 ± 0.1, compared to n F444W = 1.9 ± 0.1 for the less active field galaxies and n F444W = 2.8 ± 0.2 for the most massive field galaxies. The SMGs exhibit greater single-Sérsic fit residuals and their morphologies are more structured at 2 μm relative to 4 μm when compared to the field galaxies. This appears to be caused by significant structured dust content in the SMGs and we find evidence for dust reddening as the origin of the morphological differences by identifying a strong correlation between the F200W−F444W pixel colour and the 870 μm surface brightness using high-resolution ALMA observations. We conclude that SMGs and both massive and less massive star-forming galaxies at the same epochs share a common disc-like structure, but the weaker bulge components (and potentially lower black hole masses) of the SMGs result in their gas discs being less stable. Consequently, the combination of high gas masses and instabilities triggered either secularly or by minor external perturbations results in higher levels of activity (and dust content) in SMGs compared to typical star-forming galaxies.
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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 | 0.002 | 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 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".