Herschel and Hubble Study of a Lensed Massive Dusty Starbursting Galaxy at z ∼ 3*

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 similar to 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 mu(star) = 2.10 +/‐ 0.11 and mu(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‐circle dot yr(‐1) and a stellar mass of 6.8(‐2.7)(+0.9) x 10(11) M‐circle dot, consistent with a main sequence of star formation at z similar to 2.6. The CO observations yield a molecular gas mass of 8.3(+/‐ 1.0) x 10(10) M‐circle dot, 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 similar to 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.