Westphal-MMD11: An interacting, submillimeter luminous Lyman break galaxy

Abstract

We present new Hubble Space Telescope, high-resolution optical imaging of the submm luminous Lyman-break galaxy, Westphal-MMD11, an interacting starburst at z=2.979. The new imaging data, in conjunction with re-analysis of Keck optical and near-IR spectra, demonstrate MMD11 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 (Lambda=0.7, Omega_M=0.3, h=0.65), similar to some of the local ultra-luminous infrared galaxies (ULIGs). The lack of obvious AGN in MMD11, 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 >10^{12} L_sun bolometric luminosity of MMD11 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 MMD11 are rare, they can only be found over the restricted 2.7 < z < 3.0 range. Therefore a substantial number of MMD11-like galaxies (~<0.62 arcmin^{-2}) may exist when integrated over the likely redshift range of SCUBA sources (z=1 -5), suggesting that SCUBA sources should not necessarily be seen as completely orthogonal to optically selected galaxies.