2025A&A...694L...1P

Context. The circumgalactic medium (CGM) plays a vital role in galaxy evolution, however, studying the emission from CGM is challenging due to its low surface brightness and the complexities involved in interpreting resonant lines such as Lyman-alpha (Lyα).
Aims. The near-infrared coverage, unprecedented sensitivity, and high spatial resolution of the James Webb Space Telescope (JWST) enable us to study the optical strong lines associated with the extended Lyα “nebulae” at redshifts of 2-3. These lines serve as diagnostic tools to infer the physical conditions in the massive CGM gas reservoir of these systems.
Methods. In deep medium-band images taken by the JWST, we serendipitously discovered the [O III] emission from the CGM surrounding a massive interacting galaxy system at a redshift of z ∼ 2.8, known to be embedded in a bright extended (100 kpc) Lyα “nebula”.
Results. This is the first time that the [O III] lines have been detected from a Lyα “nebula”. The JWST images reveal that the CGM gas actually resides in narrow (∼2.5 kpc) filamentary structures with strong [O III] emission, tracing the same extent as the Lyα emission. An analysis of the [O III] suggests that the emitting CGM is fully ionized and is energetically dominated by mechanical heating. We also find that the inferred density and pressure are higher than those commonly predicted by simulations of the CGM.
Conclusions. We conclude that the observed CGM emission originates from the gas expelled by the episodic feedback processes, cooling down and enriching the CGM, while traveling a distance of at least 60 kpc. These observations demonstrate how intensive feedback processes shape gas distribution and properties in the CGM around massive halos. While access to such deep, high-resolution imaging opens up a new discovery space for investigating the CGM, it also challenges numerical simulations with respect to explaining and reproducing the exquisitely complex structures revealed by the observations.