Molecular Gas in the z = 1.2 Ultraluminous Merger GOODS J123634.53+621241.3

We report the detection of CO(2→1) emission from the z = 1.2 ultraluminous infrared galaxy (ULIRG) GOODS J123634.53+621241.3 (also known as the submillimeter galaxy GN 26). These observations represent the first discovery of high-redshift CO emission using the new Combined Array for Research in Millimeter-Wave Astronomy (CARMA). Of all high-redshift (z > 1) galaxies within the GOODS-North field, this source has the largest far-infrared (FIR) flux observed in the Spitzer 70 and 160 μm bands. The CO redshift confirms the optical identification of the source, and the bright CO(2→1) line suggests the presence of a large molecular gas reservoir of about 7 × 10¹⁰ M_☉. The infrared-to-CO luminosity ratio of L(IR)/L^'(CO) = 80 ± 30 L_☉ (K km s⁻¹ pc²)⁻¹ is slightly smaller than the average ratio found in local ULIRGs and high-redshift submillimeter galaxies. The short star formation timescale of about 70 Myr is consistent with a starburst associated with the merger event and is much shorter than the timescales for spiral galaxies and estimates made for high-redshift galaxies selected on the basis of their B − z and z − K colors.