Recent JWST observations have unveiled a large number of quiescent galaxies at z≳ 3, bringing potential challenges to current galaxy formation models. Since star formation is expected to be fed by external gas accretion, knowledge about the circumgalactic media (CGM) of these galaxies is essential to understanding how they quench. In this work, we present the discovery of a massive, passive galaxy (M_⋆ ≃ 10^ 11, M_ _ within the MUSE Quasar Nebula 01 (MQN01) large-scale structure at z≃ 3. 25, containing one of the largest overdensities of galaxies and active galactic nuclei (AGNs) found so far at z≳ 3. This passive galaxy has a star formation rate of 4^ +6 -2, M_ =0. 34 and α_ = 4 M_). Surprisingly, it is located at the center of a large cool gas reservoir, as traced by bright Lyα and Hα emission. Deep multiwavelength information unique to this field, including spectroscopic and X-ray observations, suggests that an external mechanism could keep this cool gas reservoir in a dynamically hot, turbulent state, thus reducing its ability to efficiently accumulate within the galaxy. In particular, we discuss the possibility that the agent of this external energy injection is the AGN jet from a nearby star-forming galaxy located at a projected distance of 48 kpc and detected in both X-ray and radio. Additional or alternative energy injection mechanisms could involve the gravitational interaction between these two galaxies. In all scenarios, the elevated ionizing field provided by the AGN overdensity, including the nearby AGN, can illuminate the passive galaxy's cool CGM and make it visible through fluorescent emission. Our study demonstrates that the star formation rates of high-redshift galaxies could be substantially reduced and maintained at a low level even within gas-rich and overdense environments in particular situations. placing it more than 1 dex below the star-forming main sequence, and it has no detectable molecular gas (M_ <2 M_ window, if assuming r_ H2 10^ 10 within a 700, km s -1 41 CO K^ -1 km^ -1 s pc^ 2 Chandra
Wang et al. (2026) studied this question.