GA-NIFS: The core of an extremely massive protocluster at the epoch of reionisation probed with JWST/NIRSpec
Bibliographic record
Abstract
Context. The SPT0311–58 system resides in a massive dark-matter halo at z ∼ 6.9. It hosts two dusty galaxies (E and W) with a combined star formation rate (SFR) of ∼3500 M ⊙ yr −1 , mostly obscured and identified by the rest-frame IR emission. The surrounding field exhibits an overdensity of submillimetre sources, making it a candidate protocluster. Aims. Our main goal is to characterise the environment and the properties of the interstellar medium (ISM) within this unique system. Methods. We used spatially resolved low-resolution ( R = 100) and high-resolution ( R = 2700) spectroscopy provided by the JWST/NIRSpec Integral Field Unit to probe a field of ∼17 × 17 kpc 2 around this object, with a spatial resolution of ∼0.5 kpc. Results. These observations reveal ten new galaxies at z ∼ 6.9 characterised by dynamical masses spanning from ∼10 9 to 10 10 M ⊙ and a range in radial velocity of ∼1500 km s −1 , in addition to the already known E and W galaxies. The implied large number density ( ϕ ∼ 10 4 Mpc −3 ) and the wide spread in velocities confirm that SPT0311–58 is at the core of a protocluster immersed in a very massive dark-matter halo of ∼(5 ± 3) × 10 12 M ⊙ , and therefore represents the most massive protocluster ever found at the epoch of reionisation (EoR). We also studied the dynamical stage of its core and find that it is likely not fully virialised. The galaxies in the system exhibit a wide range of properties and evolutionary stages. The contribution of the ongoing H α -based unobscured SFR to the total star formation (SF) varies significantly across the galaxies in the system. Their ionisation conditions range from those typical of the field galaxies at similar redshift recently studied with JWST to those found in more evolved objects at lower redshift, with log([OIII]/H β ) varying from ∼0.25 to 1. The metallicity spans more than 0.8 dex across the FoV, reaching nearly solar values in some cases. The detailed spatially resolved spectroscopy of the E galaxy reveals that it is actively assembling its stellar mass, showing inhomogeneities in the ISM properties at subkiloparsec scales, and a metallicity gradient (∼0.1 dex kpc −1 ) that can be explained by accretion of low metallicity gas from the intergalactic medium. The kinematic maps also depict an unsettled disc characterised by deviations from regular rotation, elevated turbulence, and indications of a possible precollision minor merger. Conclusions. These JWST/NIRSpec IFS observations confirm that SPT0311–58 is at the core of an extraordinary protocluster, and reveal details of its dynamical properties. They also unveil and provide insights into the diverse properties and evolutionary stages of the galaxies residing in this unique environment.
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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) | 0.001 | 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".