A Detailed Gravitational Lens Model Based on Submillimeter Array and Keck Adaptive Optics Imaging of a Herschel-ATLAS Submillimeter Galaxy at z = 4.243
We present high-spatial resolution imaging obtained with the Submillimeter Array (SMA) at 880 ?m 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 ?0farcs6) resolve the dust emission into multiple lensed images, while the Keck AO K S-band data (angular resolution ?0farcs1) resolve the lens into a pair of galaxies separated by 0farcs3. 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 ? = 4.1 ± 0.2 and has an intrinsic infrared (IR) luminosity of L IR = (2.1 ± 0.2) × 1013 L &sun;. 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 ?IR = (3.4 ± 0.9) × 1011 L &sun; kpc-2, 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 ?E1 = 0.57 ± 0.01 and ?E2 = 0.40 ± 0.01 that imply masses of M lens1 = (7.4 ± 0.5) × 1010 M &sun; and M lens2 = (3.7 ± 0.3) × 1010 M &sun;. 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. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
