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\to 0) by GBT and from detection
of {CO} (3\to 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× {10}11
{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) × 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.
Herschel is an ESA space observatory with science instruments provided
by European-led Principal Investigator consortia and with important
participation from NASA.