CO (J=6-5) observations of the quasar SDSS 1044-0125 at z=5.8

We present a result of CO (J = 6-5) observations of a quasar SDSSp J104433. 04-012502.2 at z = 5.8. Ten days of observations with the Nobeyama Millimet er Array yielded an rms noise level of similar to 2.1 mJy beam(-1) in a fre quency range from 101.28 GHz to 101.99 GHz at a velocity resolution of 120 km s(-1). No significant clear emission line was detected in the observed f ield and frequency range. The three-sigma upper limit on the CO (J = 6-5) l uminosity of the object is 2.8 x 10(10) K km s(-1) pc(2), corresponding to a molecular gas mass of 1.2 x 10(11) M-circle dot, if a conversion factor o f 4.5 M-circle dot (K km s(-1) pc(2))(-1) is adopted. The obtained upper li mit on the CO luminosity is slightly smaller than those observed in quasars at z = 4-5 toward which CO emissions are detected.