Dense Galaxies Are Carving Out A Bubble in the Early Universe

The James Webb Space Telescope (JWST) made groundbreaking discoveries in the early universe, revealing dense galaxy clusters that could explain the reionization process. The study, based on the JADES survey, identified a galaxy overdensity candidate at redshift z ≈ 10.5, containing 18 galaxies in a co-moving group. The overdensity is 4 times denser than the field average and accounts for one-third of the star formation rate in a specific field. The researchers found that the galaxies in this overdensity have close companions and substructures, indicating interactions. Their stellar masses and star formation rates are higher than typical, but consistent with high-redshift expectations. The detection of Lyman-alpha radiation, which is normally blocked by neutral hydrogen, shows spatial variation, suggesting the formation of an ionizing bubble.

• "The galaxy overdensity candidate at z ≈ 10.5 contains 18 galaxies in a co-moving group, with a number density 4 times higher than the field expectation."
• "The overdensity is on the western side of the GOODS-S field, about 4 times as dense as the field average."
• "The Lyman-alpha radiation shows spatial variation, consistent with the formation of an ionizing bubble with radius ∼6 cMpc."

This finding could provide evidence for the earliest stages of cosmic reionization, where galaxy overdensities carved out bubbles in the neutral hydrogen of the early universe. The spatial variation in Lyman-alpha transmission suggests that the radiation is reaching the boundary of a reionized bubble. The detection is a rare laboratory to study the structure of ionizing bubbles. The authors emphasize that the findings are based solely on spectroscopy and will be tested with future observations using the JWST and ALMA.

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