James Webb Space Telescope Feed Post

GA-NIFS: The core of an extremely massive proto-cluster at the Epoch of Reionization probed with JWST/NIRSpec

a): NIRSpec image generated collapsing the R100 datacube in the 3.0-3.8 µm spectral range (see text). The continuum emitting sources, whose spectra indicate they are at z ~ 6.9, are identified with yellow labels (i.e., C1, C2, C3, E). In the E galaxy we distinguish several sub-regions (ES, ENa,b,c). Sources that according to their spectra are at lower z (i.e., lz1, lz2, lz3) are labeled in cyan, along with the foreground lens galaxy. The red iso-contours (in red) correspond to 5, 10, 15, 30, and 100 s values. (b): [OIII] emission image at z ~ 6.9 obtained from the R100 datacube (see text for specific spectral ranges). Six line-emitting sources that were not detected in the continuum map (panel a), are identified in this map as z ~ 6.9 sources and labeled in yellow (L1 to L6). White iso-lines corresponds to 3, 5, 10, and 15 s. Here, and in panels c, d, and e, the red-contours are the same as in panel a, after removing the ones for the lens galaxy for clarity. (c): Same as panel (b) for the Ha emission. (d): MIRI image at 10 µm, after subtracting the lens (Álvarez-Márquez et al. 2023). (e): ALMA continuum at 160 µm. We mark clumps E1 – E4 identified by Spilker et al. (2022). (f): ALMA map of the [CII]?158 line. The white isolines correspond to the Ha emission. Fig. 3 identify the targets and their apertures ( for details see Appendix A). The green straight lines in all the pannels indicate the border of the NIRSpec IFU FoV. Abstract: 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 Msun/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 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, characterised by dynamical masses spanning from ~10^9 to 10^10 Msun and a range in radial velocities 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, indicate that SPT0311-58 is at the core of a proto-cluster, immersed in a very massive dark matter halo of ~ 6 x 10^12 Msun. We study the dynamical stage of the system and find that it likely is not fully virialized, although most of the galaxies are gravitationally bound to the halo. The galaxies exhibit a great diversity of properties. We derive their ongoing Halpha-based unobscured SFR, and find that its contribution to the total SF varies significantly across the galaxies in the system. Their ionization conditions range from those typical of galaxies at similar redshift recently studied with JWST to those found in lower redshift objects. The metallicity spans more than 0.8 dex across the FoV, reaching in some cases nearly solar values. The detailed IFU spectroscopy of the E galaxy reveals that it is actively assembling its stellar mass, showing a metallicity gradient (~ 0.1 dex/kpc) that can be explained by accretion of low metallicity gas from the intergalactic medium. The kinematic maps indicate departures from regular rotation, high turbulence, and a possible pre-collision minor merger. (Abridged)