2025ApJ...980...20M

We present $0\mathop{.}\limits^{^{\prime\prime} }026$ (140 pc) resolution Atacama Large Millimeter/submillimeter Array observations of [C II] 158 μm and dust continuum emission of the z = 6.6 quasar J0305-3150, resolved over ∼​​​​​​300-400 independent resolution elements. The dust continuum emission is compact with ∼80% recovered within $r\lt 0\mathop{.}\limits^{^{\prime\prime} }3$ (1.6 kpc), whereas the [C II] emission profile is composed of a central Gaussian ($r\lt 0\mathop{.}\limits^{^{\prime\prime} }4$, i.e., <2.2 kpc) and an extended component (detected up to ∼10 kpc at >3σ). We infer a direct contribution of the quasar to the observed 260 GHz continuum S_ν,QSO/S_ν,QSO + Host_ ≲ 1%. We report the detection of far-infrared (FIR)-detected star-forming clumps with r < 200 pc and properties similar to that of rest-frame UV-optical clumps reported in the literature. The 200 pc resolved [C II]/FIR ratio follows the global relation with the FIR surface brightness established in low- and high-redshift galaxies, even at the quasar location. We find that dust continuum is emitted in regions of $\unicode{x0007E}0^{\prime\prime} \,.02-0^{\prime\prime} \,.04$ consistent with the size of photodissociation regions (PDRs), whereas 50% of the [C II] originates from larger physical scales (θ ≳ 2″). The large-scale [C II] emission presents a velocity gradient aligned with a nearby companion with perturbed kinematics, and misaligned with the kinematics of the small-scale emission. The absence of significant [C II] emission by structures with physical scale ≲ 1 kpc implies that [C II] emission is not produced in dense PDRs located at the boundary of giant molecular clouds. We argue instead that [C II] is produced in low-density PDRs in the interstellar medium and diffuse H I gas tidally stripped during the ongoing merger.