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

Abstract: 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 $z\sim6.4$ quasar PSOJ183+05. We find clumpy [CII] emission, tracing gas up to a $\sim6$ 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 $\dot{M}{\rm of}\sim930$ M$\odot$ yr$^{-1}$, 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. We find that neither the high-velocity component nor the extended CGM emission in PSOJ183+05 are recovered when using the high-resolution dataset alone, which may explain the conflicting results reported regarding [CII] sizes and the detection of outflows at $z\gtrsim6$. Combining multi-configuration 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.