ALMA reveals bright circumgalactic emission and a biconical outflow in z~6.4 quasar PSOJ183+05

Understanding gas flows between galaxies and their surrounding circum-galactic medium (CGM) is crucial to unveil the mechanisms regulating galaxy evolution, especially in the early Universe. However, observations of the CGM around massive galaxies at z>6 remain limited, particularly in the cold gas phase. In this work, we present multi-configuration ALMA observations of [CII]$\lambda158,\mu$m and millimetre continuum emission in the z~6.4 quasar PSOJ183+05, to trace the cold CGM and investigate the presence of outflows. We find clumpy [CII] emission, tracing gas up to a ~6 kpc radius, consistent with the interface region between the interstellar medium (ISM) and CGM. The [CII] kinematics shows a rotating disk and a high-velocity, biconical outflow extending up to 5 kpc. The inferred mass outflow rate is ~930 MSun/yr, among the highest at z>6, and comparable to the star-formation rate. These findings suggest that quasar-driven outflows can rapidly transfer energy and momentum to the CGM, without immediately quenching star formation in the host galaxy ISM. This supports a delayed feedback scenario, in which outflows reshape CGM conditions and regulate future gas accretion over longer timescales. Combining high-resolution and sensitive ALMA data with observations from JWST and MUSE will be crucial to map the CGM across its different phases and build a comprehensive picture of the baryon cycle in the first massive galaxies.