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Arxiv: GA-NIFS: The core of an extremely massive proto-cluster at the Epoch of Reionization probed with JWST/NIRSpec Published: 12/1/2023 10:04:27 PM Updated: 4/19/2024 8:04:13 PM

Paper abstract: The SPT0311-58 system resides in a massive dark matter halo at z ~ 6.9. Ithosts two dusty galaxies (E and W) with a combined star formation rate of ~3500Msun/yr. Its surrounding field exhibits an overdensity of sub-mm sources,making it a candidate proto-cluster. We use spatially-resolved spectroscopy provided by the JWST/NIRSpec IntegralField Unit (IFU) to probe a field of view (FoV) ~ 17 x 17 kpc^2 around thisobject. These observations have revealed ten new galaxies at z ~ 6.9, characterisedby dynamical masses spanning from ~10^9 to 10^10 Msun and a range in radialvelocities of ~ 1500 km/s, in addition to the already known E and W galaxies.The implied large number density, and the wide spread in velocities, indicatethat SPT0311-58 is at the core of a proto-cluster, immersed in a very massivedark matter halo of ~ 5 x 10^12 Msun. Hence, it represents the most massiveproto-cluster ever found at the EoR. We also study the dynamical stage of thesystem and find that it likely is not fully virialised. The galaxies exhibit a great diversity of properties showing a range ofevolutionary stages. We derive their ongoing Ha-based unobscured SFR, and findthat its contribution to the total SF varies significantly across the galaxiesin the system. Their ionization conditions range from those typical of fieldgalaxies at similar redshift recently studied with JWST to those found in moreevolved objects at lower z. The metallicity spans more than 0.8 dex across theFoV, reaching nearly solar values in some cases. The detailed IFU spectroscopyof the E galaxy reveals that it is actively assembling its stellar mass,showing sub-kpc inhomogeneities, and a metallicity gradient that can beexplained by accretion of low metallicity gas from the IGM. The kinematic mapsindicate departures from regular rotation, high turbulence, and a possiblepre-collision minor merger. (Abridged)