2003A&A...409L..41W

We observed the upper fine structure line of neutral carbon, C I(³P₂-³-0.8mmP₁) (ν_rest=809GHz), the ¹²CO(J=3-2) line (ν_rest=345GHz) and the 1.2mm continuum emission from H1413+117 (Cloverleaf quasar, z=2.5) using the IRAM interferometer. Together with the detection of the lower fine structure line (Barvainis et al., 1997ApJ...484..695B), the Cloverleaf quasar is now only the second extragalactic system, besides M82, where both carbon lines have convincingly been detected. Our analysis shows that the carbon lines are optically thin and have an excitation temperature of T_ex≃30K. CO is subthermally excited and the observed line luminosity ratios are consistent with n(H₂)≃10^3–4cm^–3 at T_kin=30-50K. Using three independent methods (C I, dust, CO) we derive a total molecular gas mass (corrected for magnification) of M(H₂)≃1.2±0.3x10¹⁰M_☉. Our observations suggest that the molecular disk extends beyond the region seen in CO(7-6) to a zone of more moderately excited molecular gas that dominates the global emission in C I and the low J CO lines.