2003ApJ...584..633G

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 implies a total dynamical mass of ≥3x10¹¹sin\ul -2ih^–1_0.7M_☉within an intrinsic radius of 8h^–1_0.7kpc, 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.