2017ApJ...844...82N

We present the results of combined deep Keck/NIRC2, HST/WFC3 near-infrared, and Herschel far-infrared observations of an extremely star-forming dusty lensed galaxy identified from the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS J133542.9+300401). The galaxy is gravitationally lensed by a massive WISE-identified galaxy cluster at z ∼ 1. The lensed galaxy is spectroscopically confirmed at z = 2.685 from detection of CO (1→0) by GBT and from detection of CO (3→2) obtained with CARMA. We use the combined spectroscopic and imaging observations to construct a detailed model of the background dusty lensed submillimeter galaxy (SMG), which allows us to study the source plane properties of the target. The best-fit lens model provides magnifications of µ_star = 2.10 ± 0.11 and µ_dust = 2.02 ± 0.06 for the stellar and dust components, respectively. Multiband data yield a magnification-corrected star formation rate of 1900(±200) M_☉ yr^–1 and a stellar mass of 6.8_–2.7^+0.9×10¹¹ M_☉, consistent with a main sequence of star formation at z ∼ 2.6. The CO observations yield a molecular gas mass of 8.3(±1.0) x 10¹⁰ M_☉, similar to the most massive star-forming galaxies, which together with the high star formation efficiency, are responsible for the intense observed star formation rates. The lensed SMG has a very short gas depletion timescale of ∼40 Myr. The high stellar mass and small gas fractions observed indicate that the lensed SMG likely has already formed most of its stellar mass and could be a progenitor of the most massive elliptical galaxies found in the local universe.