2025ApJ...990L..24P

Environmental quenching-where interactions with other galaxies and/or the intracluster medium suppress star formation in low-mass galaxies-has been well established as the primary driver behind the formation of the red sequence for low-mass galaxies within clusters at low redshift (z < 1). However, it remains unclear whether these mechanisms are active at higher redshifts in protocluster environments that are not yet fully virialized. In large part, this regime has remained unexplored due to observational limitations; however, JWST has recently opened a new window into the role of environmental quenching on low-mass (log(M_⋆/M_⊙) < 9.0) galaxies at cosmic noon (2 < z < 3). Here, we leverage the deep imaging and R ∼ 15 spectrophotometry enabled by the 20 band JWST/NIRCam data from the UNCOVER and MegaScience programs to examine environmental quenching in a newly discovered z ≈ 2.58 protocluster. We compare the star formation histories of 19 low-mass quiescent galaxies in the protocluster to a matched sample of 18 in the field and find no significant differences. This similarity extends to galaxy sizes and quenched fractions, which also show no significant differences between the two environments across the full stellar mass range (8.5 < log(M_⋆/M_⊙) ≤ 11.0). This indicates that the protocluster has not yet accelerated quenching relative to the field and is consistent with expectations that z > 2 protoclusters have yet to virialize and develop a dense enough environment required to efficiently quench low-mass galaxies.