We report a galaxy overdensity candidate at z≈10.5 in the JWST Advanced Deep Extragalactic Survey (JADES). This overdensity contains 18 galaxies with consistent photometric redshifts and robust F115W dropouts within 8 comoving Mpc in projection. The galaxy number density is four times higher than the field expectation, accounting for one-third of comparably bright galaxies and nearly 50% of the total star formation rate at 10<zphot<12 in the GOODS-S field. Two compact members of the overdensity show potential Balmer breaks suggestive of evolved stellar populations or little red dots (LRDs). One-third of galaxies have close companions or substructures within 1 kpc at consistent photometric redshifts, implying more frequent interactions in an overdense environment. Most galaxies have stellar masses of 0.6-3×108M⊙, half-light radii of ∼200 pc, and star formation rates of ∼5 M⊙yr−1, with no significant deviation from typical high-redshift scaling relations. We find tentative evidence for a spatially varying Lyα transmission inferred photometrically, consistent with an emerging ionized bubble. This overdensity provides a rare opportunity for probing the environmental impact on galaxy evolution and the onset of cosmic reionization within the first 500 Myr.
@article{arxiv.2601.15960,
title = {JADES: A Prominent Galaxy Overdensity Candidate within the First 500 Myr},
author = {Zihao Wu and Daniel J. Eisenstein and Benjamin D. Johnson and Kevin Hainline and William M. Baker and Andrew J. Bunker and Alex J. Cameron and Emma Curtis-Lake and A. Lola Danhaive and Ryan Hausen and Jakob M. Helton and Zhiyuan Ji and Tobias J. Looser and Roberto Maiolino and Petra Mengistu and Pierluigi Rinaldi and Brant E. Robertson and Fengwu Sun and Sandro Tacchella and James A. A. Trussler and Christina C. Williams and Christopher N. A. Willmer and Joris Witstok},
journal= {arXiv preprint arXiv:2601.15960},
year = {2026}
}