2011ApJ...731L..27S

Based on broadband/narrowband photometry and Keck DEIMOS spectroscopy, we report a redshift of z = 4.64^+0.06_–0.08 for AzTEC/COSMOS 1, the brightest submillimeter galaxy (SMG) in the AzTEC/COSMOS field. In addition to the COSMOS-survey X-ray to radio data, we report observations of the source with Herschel/PACS (100, 160 µm), CSO/SHARC II (350 µm), and CARMA and PdBI (3 mm). We do not detect CO(5 ⟶ 4) line emission in the covered redshift ranges, 4.56-4.76 (PdBI/CARMA) and 4.94-5.02 (CARMA). If the line is within this bandwidth, this sets 3σ upper limits on the gas mass to ≲ 8 x10⁹ M_☉ and ≲ 5x10¹⁰ M_☉, respectively (assuming similar conditions as observed in z ∼ 2 SMGs). This could be explained by a low CO-excitation in the source. Our analysis of the UV-IR spectral energy distribution of AzTEC 1 shows that it is an extremely young ( ≲ 50 Myr), massive (M_* ∼ 10¹¹ M_☉), but compact ( ≲ 2 kpc) galaxy, forming stars at a rate of ∼1300 M_☉/yr. Our results imply that AzTEC 1 is forming stars in a "gravitationally bound" regime in which gravity prohibits the formation of a superwind, leading to matter accumulation within the galaxy and further generations of star formation.