A search for the CO (J=1-0) emission line toward the quasar H1413+117

We have searched for the CO (J = 1-0) line emission toward the gravitationa l lensed "Cloverleaf" quasar, H1413+117, at z = 2.56 using the 45-m telesco pe of Nobeyama Radio Observatory. The r.m.s. noise of the resultant spectru m was 1 sigma(rms) = 0.6 mK in T-MB or 1 6 mJy for a velocity resolution of 50 km s(-1). We obtained the 5 sigma(rms) upper limit of the velocity-inte grated CO (J = 1-0) line flux, integral S(1-0)dv less than or equal to 1.4 Jy km s(-1) The lower limit of the intrinsic ratio of the brightness temper ature is T-B[CO (J = 3-2)]/T-B[CO (J = 1-0)] greater than or equal to 0.79 at z = 2.56. This value corresponds to T-B[CO (J = 3-2)]1/T-B[CO (J = 1-0)] greater than or equal to 0.72-0.75 at z = 0 from a LVG calculation. This t emperature ratio is consistent with those in the central regions of nearby IR luminous galaxies.