Gas, dust and stars in the SCUBA galaxy, SMM J02399-0136: the EVLA reveals a colossal galactic nursery

We present new multiwavelength observations of the first submillimetre-selected galaxy (SMG) SMMJ02399-0136 at z = 2.8. These observations include mapping of the CO J = 1 -> 0 emission using elements of the Expanded Very Large Array, as well as high-resolution 1.4-GHz imaging and optical/infrared (IR) data from the Very Large Array, Hubble Space Telescope, Spitzer and Keck-I. Together, these new data provide fundamental insights into the mass and distribution of stars, gas and dust within this archetypal SMG. The CO J=1 -> 0 emission, with its minimal excitation and density requirements, traces the bulk of the metal-rich molecular gas, and reveals a molecular gas mass of similar to 10(11)M(circle dot), extending over approximately 5 arcsec (similar to 25 kpc in the source plane), although there is tentative evidence that it may be significantly larger. Our data suggest that three or more distinct structures are encompassed by this molecular gas reservoir, including the broad absorption line (BAL) quasar from which the redshift of the SMG was initially determined. In particular, the new rest-frame near-IR observations identify a massive, obscured, starburst which is coincident with a previously known Ly alpha cloud. This starburst dominates the far-IR emission from the system and requires a re-assessment of previous claims that the gas reservoir resides in a massive, extended disc around the BAL quasi-stellar object (QSO). Instead, it appears that SMMJ02399-0136 comprises a merger between a far-IR-luminous, but highly obscured starburst, the BAL QSO host and a faint third component. Our findings suggest that this archetypal SMG and its immediate environment mark a vast and complex galactic nursery and that detailed studies of other SMGs are likely to uncover a similarly rich diversity of properties.