Unveiling the Primordial Universe: A <1000 Msun Stellar Cluster at z=6.6

The formation of primordial stars and galaxies in the early universe has been a challenge for observational astronomers until recent advancements with JWST. Notably, Vanzella et al. (2023) used NIRSpec-IFU observations to study a highly magnified (>~100x) Lyman-alpha emitting arc at z=6.6, hinting at the presence of a low-mass (Mstar <1000 Msun), low-metallicity stellar cluster within the arc. This suggests it might host Population III stars formed from pristine gas. This program proposes extensive NIRSpec spectroscopy of the stellar cluster. The main goal is to confirm the existence of primordial gas at z=6.6 and ongoing Population III star formation. To achieve this, deep observations requiring 24 hours of on-source integration will be conducted. These observations aim to identify the HeII 1640 emission line, which will serve as a critical test of the Population III star formation scenario. The objectives also include establishing a more stringent upper limit on gas-phase metallicity by examining the deep spectrum around [OIII] 5007, providing stronger support for the primordial nature within the star forming regions of the stellar cluster. Furthermore, we will combine the entire suite of NIRCam images from GTO observations to obtain a stricter limit on the stellar mass of the stellar cluster, potentially down to 500 Msun. With these updated observational findings, this program will contribute to our understanding of the characteristics of Population III stellar clusters and the persistence of pristine gas conditions in the universe.