A SCUBA galaxy in the Protocluster around 53W002 at z=2.4

We analyse an 850-um SCUBA map of the environment of the z=2.39 radio galaxy 53W002, which has been shown to reside in an over-density of Ly-alpha detected galaxies. We identify four luminous submillimeter (submm) sources within a 2.3' (1.2Mpc at z=2.39) diameter area around the radio galaxy (which itself is a weak submm source). We employ a 1.4-GHz map to accurately locate the counterpart of one of these sources, SMMJ17142+5016, and identify this source with a narrow-line AGN with an extended Ly-alpha halo at z=2.390 which is member of the structure around 53W002. Hence SMMJ17142+5016 is the first spectroscopically-confirmed, submm-selected companion to a high-redshift radio galaxy. We discuss the OHS JHK spectrum of this galaxy and in addition present five new constraints on its spectral energy distribution longward of 1um, using these to estimate its bolometric luminosity as ~8x10^12 Lo, or a star formation rate of ~1000Mo/yr if young stars provide the bulk of the luminosity. This result provides direct support for the statistical detection of over-densities of SCUBA galaxies around high-redshift radio galaxies and confirms theoretical predictions that SCUBA galaxies, as the progenitors of massive ellipticals, should be strongly clustered in the highest density regions of the distant Universe.