2026ApJ...998..285R

We report the discovery of COSMOS2020-635829 as a candidate jellyfish galaxy undergoing ram pressure stripping in a (proto)cluster at z > 1. High-resolution imaging from the James Webb Space Telescope reveals a symmetric stellar disk coupled to a unilateral tail of star-forming knots to the south. Using Gemini GMOS integral field unit (IFU) observations, we show that these extraplanar continuum sources are embedded within an ionized gas tail that is kinematically connected to the disk of COSMOS2020-635829. If confirmed, this represents the highest-redshift discovery of a ram-pressure stripped ionized gas tail. The tail sources are characterized by extremely young stellar populations (≲100 Myr), have stellar masses of ∼10⁸M_⊙, and star formation rates of 0.1-1 M_⊙ yr^–1. This work shows that ram-pressure stripping can potentially perturb group and cluster galaxies at z > 1 and may contribute to environmental quenching even near Cosmic Noon.