CO EMISSION FROM THE Z=3.137 DAMPED LY-ALPHA SYSTEM TOWARD PC-1643+4631A

We report the detection of CO (1 --> 0) and CO(3 --> 2) emission observed toward the quasar PC 1643 + 4631A at a redshift corresponding to the z = 3.137 damped Lyalpha system previously identified in the optical spectrum of the object. This is the highest redshift CO detection reported to date. The CO emission lines have a velocity width greater-than-or-similar-to 700 km s-1 (FWZI). The CO line luminosities are approximately 10(8) L., and the mass of molecular gas is approximately 10(12) M.. Radiative transfer calculations using a large velocity gradient model imply a gas kinetic temperature of approximately 30 K. The models and observations together indicate that the angular size of the higher excitation CO(3 --> 2) emission region is approximately 0.3-0.5 times that of the lower excitation CO(1 --> 0) emission region; that is, the gas is appreciably clumped.