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 ≈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 μ = 4.1 ± 0.2 and has an intrinsic
infrared (IR) luminosity of L IR = (2.1 ± 0.2) ×
1013 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 ΣIR = (3.4
± 0.9) × 1011 L ⊙
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 θE1 = 0.57 ± 0.01 and
θE2 = 0.40 ± 0.01 that imply masses of M
lens1 = (7.4 ± 0.5) × 1010 M
⊙ and M lens2 = (3.7 ± 0.3) ×
1010 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.
Herschel is an ESA space observatory with science instruments provided
by European-led Principal Investigator consortia and with important
participation from NASA.