MOLECULAR GAS IN A SUBMILLIMETER GALAXY AT z=4.5: EVIDENCE FOR A MAJOR MERGER AT 1 BILLION YEARS AFTER THE BIG BANG

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 similar to 1000 km s(-1), an integrated line flux of 0.66 Jy km s(-1), and a CO luminosity of 3.2 x 10(10) L(circle dot). 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 x 10(10) M(circle dot) assuming an ULIRG-like conversion factor. From the spatial offset of the red- and blueshifted line peaks and the line width a dynamical mass of 1.1 x 10(11) M(circle dot) 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 similar to 2) submillimeter galaxies (SMGs) z similar to 2 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(circle dot) 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.