JWST Observations Reveal Massive Proto-Cluster at Epoch of Reionization
Recent observations using the James Webb Space Telescope (JWST) have provided significant insights into the SPT0311-58 system, which is located in a massive dark matter halo at a redshift of approximately 6.9. This system hosts two dusty galaxies, designated as E and W, with a combined star formation rate of about 3500 solar masses per year. The surrounding field shows an overdensity of submillimeter sources, indicating that it is a candidate for a proto-cluster.
The research utilized spatially-resolved spectroscopy from the JWST/NIRSpec Integral Field Unit (IFU) to examine a field of view measuring approximately 17 x 17 kiloparsecs around the SPT0311-58 object. The observations revealed ten new galaxies at the same redshift, characterized by dynamical masses ranging from about 10^9 to 10^10 solar masses and a variety of radial velocities, indicating a significant number density and a wide spread in velocities. This suggests that SPT0311-58 is at the core of a proto-cluster, situated within a dark matter halo estimated to be around 5 x 10^12 solar masses, marking it as the most massive proto-cluster identified at the Epoch of Reionization.
The study also examined the dynamical state of the system, concluding that it is likely not fully virialized. The galaxies within the proto-cluster exhibit diverse properties and evolutionary stages. The ongoing star formation rates vary significantly across the galaxies, and their ionization conditions range from those typical of field galaxies at similar redshifts to those found in more evolved objects at lower redshifts. The metallicity across the field varies widely, reaching nearly solar values in some instances. Notably, detailed spectroscopy of galaxy E indicated active stellar mass assembly, with inhomogeneities on sub-kiloparsec scales and a metallicity gradient attributed to the accretion of low metallicity gas from the intergalactic medium.
These findings enhance our understanding of galaxy formation and evolution during the early universe, particularly at a time when the universe was less than a billion years old. The research is documented in the paper titled "GA-NIFS: The core of an extremely massive proto-cluster at the Epoch of Reionization probed with JWST/NIRSpec" by Santiago Arribas and colleagues, available at arXiv:2312.00899.