GA-NIFS: The core of an extremely massive protocluster at the epoch of reionisation probed with JWST/NIRSpec

Context. The SPT0311-58 system resides in a massive dark-matter halo at z similar to 6.9. It hosts two dusty galaxies (E and W) with a combined star formation rate (SFR) of similar to 3500 M-circle dot 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 similar to 17 x 17 kpc2 around this object, with a spatial resolution of similar to 0.5 kpc. Results. These observations reveal ten new galaxies at z similar to 6.9 characterised by dynamical masses spanning from similar to 109 to 1010 M-circle dot and a range in radial velocity of similar to 1500 km s(-1), in ...