Possible detection of a CO emission line from a quasar at z = 2.88

We observed a high-redshift luminous radio-quiet quasar Q1235+0857 at z = 2.880 with the Nobeyama 45 m radio telescope aiming at detection of a redshifted ¹²CO (J = 3-2) emission line. We have marginally (3-5 σ significance) detected an emission-line-like feature at ∼89.8 GHz (z = 2.883) with ∼150 km s^-1 width (FWHM). Adopting the standard CO to H₂ conversion factor obtained for galactic giant molecular clouds, the CO luminosity can be roughly converted to H₂ gas mass of ∼10¹² M_⊙, which is much larger than the molecular gas content of any galaxies at preent epoch and nearly equal to the total stellar mass of a giant elliptical galaxy. Although we should note that a confirmation of the detection by an independent facility is absolutely needed, the results discussed in this Letter would support the idea that luminous quasars at high redshift are associated with the massive galaxies in their forming phase.