Spatially Resolved Millimeter Interferometry of SMM J02399−0136: AVery Massive Galaxy atz= 2.8

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Abstract
We report high-resolution millimeter mapping with the IRAM Plateau de Bure interferometer of rest-frame 335 μm continuum and CO (3-2) line emission from the z = 2.8 submillimeter galaxy SMM J02399-0136. The continuum emission comes from a ~3'' diameter structure whose elongation is approximately east-west and whose centroid is coincident within the astrometric errors with the brightest X-ray and rest-UV peak (L1). The line data show that this structure is most likely a rapidly rotating disk. Its rotation velocity of ≥420 km s-1 implies a total dynamical mass of ≥3 × 1011 sin−2 i h M☉ within an intrinsic radius of 8 h kpc, most of which is plausibly in the form of stars and gas. SMM J02399-0136 is thus a very massive system, whose formation at z ~ 3 is not easy to understand in current cold dark matter hierarchical merger cosmogonies.