Westphal-MMD 11: An Interacting, Submillimeter Luminous Lyman Break Galaxy

We present new Hubble Space Telescope, high-resolution optical imaging of the submillimeter luminous Lyman break galaxy (LBG), Westphal-MMD 11, an interacting starburst at z = 2.979. The new imaging data, in conjunction with reanalysis of Keck optical and near-IR spectra, demonstrate MMD 11 to be an interacting system of at least three components: a luminous blue source, a fainter blue source, and an extremely red object (ERO) with R-K ≳ 6. The separations between components are ~8 kpc (Λ = 0.7, Ω_M = 0.3, h = 0.65), similar to some of the local ultraluminous infrared galaxies (ULIGs). The lack of obvious active galactic nucleus in MMD 11, along with the fragmented, early-stage merger morphology, suggest a young forming environment. While we cannot unambiguously identify the location of the far-IR emission within the system, analogy to similar ULIGs suggests the ERO as the likely far-IR source. The greater than 10¹² L_☉ bolometric luminosity of MMD 11 can be predicted reasonably from its rest-frame UV properties once all components are taken into account; however, this is not typically the case for local galaxies of similar luminosities. While LBGs as red in g-R and R-K as MMD 11 are rare, they can only be found over the restricted 2.7 < z < 3.0 range. Therefore, a substantial number of MMD 11-like galaxies (≃0.62 arcmin^-2) may exist when integrated over the likely redshift range of Submillimeter Common-User Bolometric Array (SCUBA) sources (z = 1-5), suggesting that SCUBA sources should not necessarily be seen as completely orthogonal to optically selected galaxies.