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We report the detection of CO J = 2→1, 5→4, and 6→5 emission in the highest-redshift submillimeter galaxy (SMG) AzTEC-3 at z = 5. 298, using the Expanded Very Large Array and the Plateau de Bure Interferometer. These observations ultimately confirm the redshift, making AzTEC-3 the most submillimeter-luminous galaxy in a massive z ≃ 5. 3 protocluster structure in the COSMOS field. The strength of the CO line emission reveals a large molecular gas reservoir with a mass of 5. 3 × 10^ (10) (α_ (CO) /0. 8) M_☉ sun, which can maintain the intense 1800 M_☉ sun yr^ (–1) starburst in this system for at least 30 Myr, increasing the stellar mass by up to a factor of six in the process. This gas mass is comparable to "typical" z ~ 2 SMGs and constitutes ≳80% of the baryonic mass (gas+stars) and 30%-80% of the total (dynamical) mass in this galaxy. The molecular gas reservoir has a radius of 4 SMGs and z > 4 quasar host galaxies, which perhaps trace different evolutionary stages. The discovery of a massive, metal-enriched gas reservoir in an SMG at the heart of a large z = 5. 3 protocluster considerably enhances our understanding of early massive galaxy formation, pushing back to a cosmic epoch where the universe was less than 1/12 of its present age.
Riechers et al. (Mon,) studied this question.