James Webb Space Telescope Feed Post

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: 12/1/2023 10:04:27 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 (SFR) of~3500 Msun/yr. Its surrounding field exhibits an overdensity of sub-mm sources,making it a candidate proto-cluster. We use spatially-resolved spectroscopyprovided by the JWST/NIRSpec Integral Field Unit (IFU) to probe a field of view(FoV) ~ 17 x 17 kpc^2 around this object, with a spatial resolution ~ 0.5 kpc. 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 ~ 6 x 10^12 Msun. We study the dynamical stage of thesystem and find that it likely is not fully virialized, although most of thegalaxies are gravitationally bound to the halo. The galaxies exhibit a greatdiversity of properties. We derive their ongoing Halpha-based unobscured SFR,and find that its contribution to the total SF varies significantly across thegalaxies in the system. Their ionization conditions range from those typical ofgalaxies at similar redshift recently studied with JWST to those found in lowerredshift objects. The metallicity spans more than 0.8 dex across the FoV,reaching in some cases nearly solar values. The detailed IFU spectroscopy ofthe E galaxy reveals that it is actively assembling its stellar mass, showing ametallicity gradient (~ 0.1 dex/kpc) that can be explained by accretion of lowmetallicity gas from the intergalactic medium. The kinematic maps indicatedepartures from regular rotation, high turbulence, and a possible pre-collisionminor merger. (Abridged)