2006ApJ...651...46W

We present a detection of [C I] ³P₁-³P₀emission in the lensed quasar APM 08279+5255 at z=3.91 using the IRAM Plateau de Bure interferometer. The [C I] line velocity and width are similar to the values of previously detected high-J CO and HCN lines in this source, suggesting that the emission from all of these species arises from the same region. The apparent luminosity of the [C I] line is L'_CI_=(3.1±0.4)x10¹⁰ K.km/s.pc², which implies a neutral carbon mass M_CI_=(4.4±0.6)/mx10⁷ M_☉, where m is the lensing magnification factor. The [C I] line luminosity is consistent with the large molecular gas mass inferred from the nuclear CO line luminosity (∼10¹¹/m.M_☉). We also present an upper limit on the H₂O 1₁₀-1₀₁line luminosity in APM 08279+5255 of L'_H2_O<1.8x10¹⁰ K.km/s.pc² (3 σ).