Gas and dust in the Cloverleaf quasar at redshift 2.5

Abstract

We observed the upper fine structure line of neutral carbon, C I( 3 P2! 3 P1 )( rest = 809 GHz), the 12 CO(J= 3!2) line (rest= 345 GHz) and the 1.2 mm continuum emission from H1413+117 (Cloverleaf quasar, z= 2:5) using the IRAM inter- ferometer. Together with the detection of the lower fine structure line (Barvainis et al. 1997), the Cloverleaf quasar is now only the second extragalactic system, besides M 82, where both carbon lines have convincingly been detected. Our analysis shows that the carbon lines are optically thin and have an excitation temperature of Tex 30 K. CO is subthermally excited and the observed line luminosity ratios are consistent with n(H2) 10 3 4 cm 3 at Tkin= 30-50 K. Using three independent methods (C I, dust, CO) we derive a total molecular gas mass (corrected for magnification) of M(H2) 1.2 0.3 10 10 M. 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. described by a 3-level system. This allows us to derive its ex- citation and to constrain the physical gas conditions by obser- vations of the C I( 3 P1! 3 P0) and C I( 3 P2! 3 P1) transitions only. We compare our results from C I with estimates based on ther- mal dust emission and CO. We use H0= 75 km s 1 Mpc 1 and q0= 0:5.