We report the detection of the 3P1 to 3P0 fine-structure line of neutral carbon in the z=4.12 quasar PSS 2322+1944, obtained at the IRAM Plateau de Bure interferometer. The CI 3P1-3P0 line is detected with a signal-to-noise ratio of about 6 with a peak intensity of about 2.5 mJy and a velocity-integrated line flux of 0.81+-0.12 Jy.km/s. Assuming an excitation temperature of 43 K (equal to the dust temperature), we derive a mass of neutral carbon (corrected for magnification) of about 1.2e7 Msun. In PSS 2322+1944, the cooling due to C is about 6 times smaller than for CO, whereas the CO and C cooling represents about 1e-4 of the far-infrared continuum and more than half of the cooling due to C+.
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