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 circumgalactic 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 multiconfiguration Atacama Large Millimeter/submillimeter Array (ALMA) observations of C II λ 158 μ m and millimeter continuum emission in the z ∼ 6.4 quasar PSOJ183+05. We find clumpy C II emission, tracing gas up to a ∼6 kpc radius, consistent with the interface region between the interstellar medium (ISM) and CGM. The C II kinematics shows a rotating disk and a high-velocity, biconical outflow extending up to 5 kpc. The inferred mass outflow rate is M ̇ of ∼ 930 M ⊙ 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 data set alone, which may explain the conflicting results reported regarding C II sizes and the detection of outflows at z ≳ 6. Combining multiconfiguration ALMA data with observations from JWST and the Multi Unit Spectroscopic Explorer 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.