We report the detection of CO molecular line emission in the z=4.5 millimeter-detected galaxy COSMOS_J100054+023436 ( hereafter : J1000+0234 ) using the IRAM Plateau de Bure interferometer ( PdBI ) and NRAO ’ s Very Large Array ( VLA ) .
The ^ { 12 } CO ( 4-3 ) line as observed with PdBI has a full line width of \sim 1000 \ > { km } { s } ^ { -1 } , an integrated line flux of 0.66 Jy \ > { km } { s } ^ { -1 } , and a CO luminosity of 3.2 \times 10 ^ { 10 } \ > { L _ { \odot } } .
Comparison to the 3.3 \sigma detection of the CO ( 2-1 ) line emission with the VLA suggests that the molecular gas is likely thermalized to the J=4-3 transition level .
The corresponding molecular gas mass is 2.6 \times 10 ^ { 10 } \ > { M _ { \odot } } assuming an ULIRG-like conversion factor .
From the spatial offset of the red- and blue-shifted line peaks and the line width a dynamical mass of 1.1 \times 10 ^ { 11 } \ > { M _ { \odot } } is estimated assuming a merging scenario .
The molecular gas distribution coincides with the rest-frame optical and radio position of the object while being offset by 0.5 ” from the previously detected Ly \alpha emission .
J1000+0234 exhibits very typical properties for lower redshift ( z \sim 2 ) sub-millimeter galaxies ( SMGs ) and thus is very likely one of the long sought after high redshift ( z > 4 ) objects of this population .
The large CO ( 4-3 ) line width taken together with its highly disturbed rest-frame UV geometry suggest an ongoing major merger about a billion years after the Big Bang .
Given its large star formation rate ( SFR ) of > 1000 \ > { M _ { \odot } } yr ^ { -1 } and molecular gas content this object could be the precursor of a ’ red-and-dead ’ elliptical observed at a redshift of z=2 .