WITNESSING THE BIRTH OF THE RED SEQUENCE: ALMA HIGH-RESOLUTION IMAGING OF [C II] AND DUST IN TWO INTERACTING ULTRA-RED STARBURSTS AT z=4.425

Exploiting the sensitivity and spatial resolution of the Atacama Large Millimeter/submillimeter Array, we have studied the morphology and the physical scale of the interstellar medium-both gas and dust-in SGP. 38326, an unlensed pair of interacting starbursts at z = 4.425. SGP 38326 is the most luminous star bursting system known at z > 4, with a total IR luminosity of L-IR similar to 2.5 x 10(13) L-circle dot and a star formation rate of similar to 4500M(circle dot) yr(-1) .SGP 38326 also contains a molecular gas reservoir among the most massive yet found in the early universe, and it is the likely progenitor of a massive, red-and-dead elliptical galaxy at z similar to 3 Probing scales of similar to 0.1 or similar to 800 pc we find that the smooth distribution of the continuum emission from cool dust grains contrasts with the more irregular morphology of the gas, as traced by the [C II] fine structure emission. The gas is also extended over larger physical scales than the dust. The velocity information provided by the resolved [C II] emission reveals that the dynamics of the two interacting components of SGP 38326 are each compatible with disk-like, ordered rotation, but also reveals an ISM which is turbulent and unstable. Our observations support a scenario where at least a subset of the most distant extreme starbursts are highly dissipative mergers of gas-rich galaxies.