2012ApJ...756..134B

We present high-spatial resolution imaging obtained with the Submillimeter Array (SMA) at 880 µm and the Keck adaptive optics (AO) system at the K_S-band of a gravitationally lensed submillimeter galaxy (SMG) at z = 4.243 discovered in the Herschel Astrophysical Terahertz Large Area Survey. The SMA data (angular resolution ~0".6) resolve the dust emission into multiple lensed images, while the Keck AO K_S-band data (angular resolution ~0".1) resolve the lens into a pair of galaxies separated by 0".3. We present an optical spectrum of the foreground lens obtained with the Gemini-South telescope that provides a lens redshift of z_lens= 0.595±0.005. We develop and apply a new lens modeling technique in the visibility plane that shows that the SMG is magnified by a factor of µ = 4.1±0.2 and has an intrinsic infrared (IR) luminosity of L_IR= (2.1±0.2)x10¹³ L_☉. We measure a half-light radius of the background source of r_s= 4.4±0.5 kpc which implies an IR luminosity surface density of Σ_IR= (3.4±0.9) x10¹¹ L_☉/kpc2, a value that is typical of z > 2 SMGs but significantly lower than IR luminous galaxies at z ∼ 0. The two lens galaxies are compact (r_lens~ 0.9 kpc) early-types with Einstein radii of θ_E1= 0.57±0.01 and θ_E2= 0.40±0.01 that imply masses of M_lens1= (7.4±0.5)x10¹⁰ M_☉ and M_lens2= (3.7±0.3) x10¹⁰ M_☉. The two lensing galaxies are likely about to undergo a dissipationless merger, and the mass and size of the resultant system should be similar to other early-type galaxies at z ∼ 0.6. This work highlights the importance of high spatial resolution imaging in developing models of strongly lensed galaxies discovered by Herschel.